ordinary level practical

ORDINARY LEVEL COMPREHENSIVE CHEMISTRY PRACTICAL GUIDE

1.

MnO4-

2. VOLUMETRIC ANALYSIS HEART OF CHEMISTRY

Al3+, Pb2+,Pb2+

CO2, NH3, SO2, HCl

3. COMMON ANIONS Cl-, SO42-, CO32-, HCO34. COMMON GASES

Mg2+, Ca2+, Ba2+, Al3+, Pb2+,Pb2+

2. NON-TRANSITION METAL CATIONS

1. TRANSITION METAL CATIONS,

Volumetric analysis is the technique of finding the concentration of the solution. In this the 1. technique TRANSITION solution of the known concentration is added repeatedly the one whose concentration is METAL to be determined CATIONS, until there is just enough of it to neutralise the other of the unknown concentration. The method is called titration. During titration, the volume of standard solution that completely reacts with the measured 2+, Fe2+, Fe3+ Cu volume of the solution under the analysis is recorded. The titration is repeated to obtain consistent titres. From consistent titre values, an average of volume of the standard solution is calculated. By us appropriate 2. NONstoichiometry (reaction ratio) obtained from the balanced equation between the reacting substances in the TRANSITION experiment, the concentration of the solution under analysis can be calculated. METAL CATIONS Volumetric analysis is performed using the following important laboratory apparatus. These include burette, pipette, conical flask, beakers, retort stand and clamp, volumetric flasks, weighing balance. 2+, Ca2+, Ba2+, Mg

Cu2+, Fe2+, Fe3+

2.1. DETAILS OF APPARATUS USED DURING TITRATION 3. COMMON a) Burette. ANIONS The burette is designed to deliver variable volumes of liquids. It is graduated from 0 to 50cm3 in units -, SO 2-, CO 2-, 4 It is then 3 of 0.10cm3. Before use, the burette is rinsed with water, then a little of solution to beCl put in it. clamped vertically and filled carefully with solution beyond the zero mark. The meniscus HCO3of- the solution is then adjusted by draining it by opening the tap. Read the lower meniscus to get the 4. COMMON GASES accurate volume of the solution. CO2, NH3, SO2, b) Pipette. HCl A pipette is designed to deliver a fixed or definite volume of a liquid such a 50, 25, 10, 5cm3. Before use, rinse the pipette with water followed by a little of the solution. The pipette is then filled by sucking the solution into it beyond the calibration mark. Close the mouth using the first finger, then adjust the 2+ MnO Cu 4meniscus to the mark by allowing the solution to flow down slowly. Then allow the accurately Fe2+ measured volume of the solution to flow into the conical flask under gravity. Do not blow; touch the side of the conical flask to allow the last drops to flow into the conical flask.

2015

c) Conical flask. The conical flask is where the pipetted solution is put; the flask must be cleaned with water. To the solution in the conical flask is added appropriate number of drops of indicator solution given. Mainly 2-3 drops are added. The indicator solutions include methyl orange, phenolphthalein indicator, indicator, etc. MUDUKU IVANbromocresol blue, bromocresol green, starch [email protected] BSci.ED,MUKd) Beaker. Facebook (Heart of chemistry) A beaker is designed to measure the varying volumes of solutions. It should be cleaned with water [email protected] Twitter (Heart of chemistry@practicals) before use. 0773860121/0701510625 e) Retort stand and clamp. HEART OF CHEMISTRY

[email protected] FACEBOOK (HEART OF CHEMISTRY)

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

1. VOLUMETRIC ANALYSIS Volumetric analysis is the technique of finding the concentration of the solution. In this technique the solution of the known concentration is added repeatedly the one whose concentration is to be determined until there is just enough of it to neutralise the other of the unknown concentration. The method is called titration. During titration, the volume of standard solution that completely reacts with the measured volume of the solution under the analysis is recorded. The titration is repeated to obtain consistent titres. From consistent titre values, an average of volume of the standard solution is calculated. By us appropriate stoichiometry (reaction ratio) obtained from the balanced equation between the reacting substances in the experiment, the concentration of the solution under analysis can be calculated. Volumetric analysis is performed using the following important laboratory apparatus. These include burette, pipette, conical flask, beakers, retort stand and clamp, volumetric flasks, weighing balance.

a. DETAILS OF APPARATUS USED DURING TITRATION f) Burette. The burette is designed to deliver variable volumes of liquids. It is graduated from 0 to 50cm3 in units of 0.10cm3. Before use, the burette is rinsed with water, then a little of solution to be put in it. It is then clamped vertically and filled carefully with solution beyond the zero mark. The meniscus of the solution is then adjusted by draining it by opening the tap. Read the lower meniscus to get the accurate volume of the solution. g) Pipette. A pipette is designed to deliver a fixed or definite volume of a liquid such a 50, 25, 10, 5cm3. Before use, rinse the pipette with water followed by a little of the solution. The pipette is then filled by sucking the solution into it beyond the calibration mark. Close the mouth using the first finger, then adjust the meniscus to the mark by allowing the solution to flow down slowly. Then allow the accurately measured volume of the solution to flow into the conical flask under gravity. Do not blow; touch the side of the conical flask to allow the last drops to flow into the conical flask. h) Conical flask. The conical flask is where the pipetted solution is put; the flask must be cleaned with water. To the solution in the conical flask is added appropriate number of drops of indicator solution given. Mainly 2-3 drops are added. The indicator solutions include methyl orange, phenolphthalein indicator, bromocresol blue, bromocresol green, starch indicator, etc. i) Beaker. A beaker is designed to measure the varying volumes of solutions. It should be cleaned with water before use. j) Retort stand and clamp. These two are used together to clamp the burette as shown below. 1.1. SOLUTIONS  Standard solution. A standard solution is one whose concentration is accurately known. The term concentration refers to the amount of solute dissolved in a specific volume of a solvent.

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One way of expressing the concentration of a solution is to state the number of moles of solute dissolved in 1000cm3 or 1litre of the solution. When one mole of a solute is dissolved in solvent (water) to make 1000cm3 of the solution, the solution is said to be a molar solution written as 1M or 1mol dm-3. This is sometimes refered to as molarity. A solution containing 5 moles of the solute in 1000cm3 or 1dm3 has a concentration of 5mol dm-3 simply written as 5M. Similarly a solution containing 0.3 moles of sulphuric acid in 1000cm3 has a concentration of 0.3M, written as 0.3M sulphuric acid. Qn. What would be the concentration/molarity of a solution containing 5moles in 2500cm3 of solution? ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................................................. Concentration in grams per litre or grams per cubic decimetres The concentration can also be expressed in grams per litre or grams per cubic decimetres written as gl1 of gdm-3 respectively. When 4g of sodium carbonate are dissolved to make 1 litre of solution, we say that the solution has a concentration of 4gl-1 or 4gdm-3 of sodium carbonate. Example 53.5g of sodium chloride were dissolved to make 2000cm3 of the solution, calculate the concentration of sodium chloride in grams per litre. (Na = 23, Cl = 35.5) Solution 1000cm3 is the standard volume equivalent to 1dm3 or 1litre 𝟏

1cm3 will be equal to 1 will be equal to 𝟏𝟎𝟎𝟎 2000cm3 will be equal to 2000 X

𝟏 𝟏𝟎𝟎𝟎

= 2dm3

2dm3 of solution contains 53.5g of NaCl 1dm3 of solution will contain

𝟓𝟑.𝟓 g 𝟐

of NaCl

=26.75gdm-3 Alternatively, Since you know how to calculate the number of moles, we can first calculate the number of moles per litre/cubic decimetre and then convert to gdm-3 as shown below. R.F.M of NaCl = 23 + 35.5 = 58.5 Therefore molar mass of NaCl = 58.5g This implies that 58.5g of NaCl contain 1 mole 𝟏

1g of NaCl will contain 𝟓𝟖.𝟓 moles 𝟏

53.5g of NaCl will contain 53.5 X 𝟓𝟖.𝟓 moles = 0.9145moles 2dm3 of solution contains 0.9145moles 1dm3 of solution will contain 0.9145⁄2 moles = 0.4573 moldm-3 = 0.4573M Therefore molarity = 0.4573M 1 mole of NaCl weighs 58.5g Therefore 0.4573moles will weigh

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𝟎.𝟒𝟓𝟕𝟑 𝐗 𝟓𝟖.𝟓 = 26.75gdm-3 𝟏

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Calculating the amount of substance in a given volume of solution As stated before, the concentration of solution is quoted in terms of mol dm-3 or gl-1. The quoted figure is called molarity (M). Given a solution of sodium hydroxide with molarity of 0.5M, it means that every 1000cm3 of that solution contains 0.5moles of sodium hydroxide. If there is uniform distribution of the solute (sodium hydroxide) in the solution and samples of different volumes of this solution are drawn from it. Qn. How can we find the amount of sodium hydroxide in each of the drawn samples? Let’s consider the example below, If solution samples of volumes 5.00, 10.00, 25.00cm3 are drawn from a 0.5M solution of sodium hydroxide, calculate the number of moles of sodium hydroxide in each of the samples. For 5.00cm3 0.5M means that 1000cm3of solution contains 0.5moles of sodium hydroxide 1.00cm3 of solution will contain

0.5 moles 1000

0.5

Therefore 5.00cm3 will contain 1000 X 5.00 moles = 0.0025moles For 10.00cm3 0.5M means that 1000cm3of solution contains 0.5moles of sodium hydroxide 0.5

1.00cm3 of solution will contain 1000 moles Therefore 10.00cm3 will contain

0.5 X 1000

10.00 moles

= 0.005moles

0.5M means that

1000cm3of

For 25.00cm3 solution contains 0.5moles of sodium hydroxide 0.5

1.00cm3 of solution will contain 1000 moles 0.5

Therefore 25.00cm3 will contain 1000 X 25.00 moles = 0.0125moles

ACID-BASE TITRATION Acid-base titration is the titration between an acid and an alkali. The reaction taking place is in this titration is called neutralisation reaction. The reaction is represented by the equation below, H+(aq) + OH-(aq) H2O(l) The progress of the reaction is determined by adding an indicator to the solution in the conical flask. At the end point, the indicator shows a sharp colour change. Students should take care when the end point is about to be reached. Add the solution from the burette drop by drop to avoid over shooting. At this level, the indicator solutions used for titration are phenolphthalein and methyl orange indicators. They show the following colours in acid and base media.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Indicator

Colour in acid medium

Colour in alkali medium

Phenolphthalein

colourless

pink

Methyl orange

Red

yellow

TITRATION PROCEDURE

a) b)

c)

d)

e)

Given a solution for titration and a set of apparatus to be used, Use a pipette to deliver appropriate volume of solution e.g 25.0, 20.0, 10.0, 5.0cm3 into a clean conical flask. The pipette must be rinsed water and the solution to be pipette. Rinse the burette with some water followed by a little of the solution to be put in the burette. Fill the burette with the solution up to slightly beyond the zero mark and allow some of the solution to flow into the tip of the burette. Read the initial burette readinds as V1cm3 Arrange the apparatus as shown below, run the solution from the burette drop wise. Use your left hand to open the burette tap and your right hand to swirl the conical flask (unless you are left handed). Stop when the indicator just changes colour. This is the end-point of the solution. Read the final burette reading as V2cm3. Subtract the initial burette reading from final burette reading to obtain the volume of solution in the burette that completely reacts with a volume of standard solution in the flask, ie V = V2 – V1. Repeat the titration several times to obtain consistent titres. Take closest titre values and determine their average. Use the average volume to calculate the concentration of the unknown using appropriate stoichiometry, or mole ratios. Reaction equation is crucial in obtaining reaction ratios of the reaction.

FILLING THE TABLE Volume of pipette =

25.0cm3

Experiment

1

2

3

4

Final burette reading (cm3)

25.40

27.00

44.90

36.80

Initial burette reading (cm3)

0.00

2.20

20.00

12.00

Volume of solution used (cm3)

25.40

24.80

24.90

24.80

Note the following,  The table must be filled to two decimal places with the last figure being a zero.  The subtraction must be correct  Take values which a close to one another to calculate the average. This enhances precision; students should know that precision does not mean accuracy. Precision is simply the closeness of the

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

measured values to one another whereas accuracy is the degree of agreement of the measured value to the accepted or accurate value.  The pipette volume must be indicated. Since the pipette is used to deliver a fixed volume. The volume is appropriately recorded to one decimal place; however there is no penalty for recording to two decimal places.

PRACTICAL SHEDULES a) Practical 1 Standardisation of sodium hydroxide with 0.1M hydrochloric acid You are provided with the following  1 burette (50ml)  2 conical flask  1 pipette (20 or 25ml)  Phenolphthalein indicator  Solution of BA1 which is 0.1M hydrochloric acid solution  Solution of BA2 which is sodium hydroxide solution You are required to determine the concentration of solution of BA2 in i. ii.

Mol dm-3 or M gdm-3 or gl-1

Procedure: Pipette 25.0 0r 20.0cm3 of BA2 into a clean conical flask. Add two drops of phenolphthalein indicator and swirl. Titrate the mixture with BA1 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below.

Volume of pipette used.................................................cm3 Experiment

1

2

3

4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA1 used (cm3) Values used to calculate the average volume of BA1 ..................................................................................................................................................................................................................... .......................................................................................................................... Average volume of BA1

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

i.

ii.

iii.

iv.

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................. Calculate, Number of moles of BA1 that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................................................... The number of moles of BA2 that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... The concentration of BA2 in mol dm-3 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................................................... The concentration of BA2 that reacted in gl-1 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ....................................................................................................................................

Teachers comment and evaluation ............................................................................................................................. ..................................................................... .................................................................................................................................................................... .............................. ..................................................................................................... ........................................................................................... b) Practical 2 Standardisation of hydrochloric acid using sodium carbonate solution You are provided with the following,  BA3 which is approximately 0.2M hydrochloric acid  BA4 which is made by dissolving 10.6g of sodium carbonate to make 1litre of solution  Methyl orange indicator  1 burette  1 pipette  2 conical flasks  Stand and clamp You are required to determine the concentration of BA3 in

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

i) ii)

Mol dm-3 gl-1 Procedure, Pipette 25.0cm3 of BA4 into a clean conical flask. Add 2 drops of methyl orange indicator into it and swirl. Titrate the mixture with BA3 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below, Volume of the pipette used................................................cm3 Experiment 1 2 3 4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA3 used (cm3) Values used to calculate the average volume of BA3 ............................................................................................................................................................................................................................... ..................................................................................................... Average volume of BA3 ............................................................................................................................................................................................................................... ............................................................................................................................................................................................................................... ....................................... Calculate i)

ii)

iii)

number of moles of BA4 that reacted (Na = 23, C = 12, O = 16) ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... .................................................................................................................................................... the number of moles of BA3 that reacted ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ..................................................................................................................................................... the concentration of BA3 in mol dm-3 ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... .......................................................................................................................................................................................................

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iv)

....................................................................................................................................................................................................... ...... the concentration of BA3 in gl-1(H = 1, Cl = 35.5) ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ............................................................................................. Teachers comment and evaluation ............................................................................................................................. .................................. ............................................................................................................................................................... ............................................................................................................................. .................................. .......................................................................................................

c) practical 3 Determination of relative atomic mass of metal M in M2CO3 You are provided with the following solutions  BA1 which is 0.2M hydrochloric acid solution  BA2 which is a salt solution made by dissolving 10.6g 0f M2CO3 in 1litre of solution You are required to determine the relative atomic mass of metal M in M2CO3 Procedure, Pipette 25ml of BA2 into cleans a conical flask. Add two drops of methyl orange indicator to it and swirl. Titrate the mixture with BA1 from the burette. Repeat the titration to obtain consistent titres. Record your results in the table below, Volume..........................................................................cm 3 Experiment

1

2

3

4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA1 used (cm3) Values used to calculate the average volume of BA1 ..................................................................................................................................................................................................................... ....................................................................... The average volume of BA1 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .... Calculate,

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a) i) The number of moles of BA1 that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................... iii) write the equation of reaction between BA1 and BA2 ..................................................................................................................................................................................................................... ......................................................................... iv) write the mole ratio of the reaction ..................................................................................................................................................................................................................... ......................................................................... b) The number of moles of BA2 that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ....................... c) Calculate the molarity of BA2 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ....................... d) Calculate the relative formula mass of M2CO3 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ....................... e) Determine the relative atomic mass of M( C = 12, O = 16) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .............................................................................................................................................................. Teachers comment and evaluation ............................................................................................................................. ..................................................................... ............................................................................................................................. ..................................................................... ...................................................................................................................................................... .......................................... d) Practical 4 Determination of atomic mass of X in an acid

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You are provided with the following, BA3 which is a solution containing 1.7g of OH- ions per litre BA4 which is a dibasic acid H2X containing 9.8gl-1 You are required to determine the atomic mass of X in the acid (H = 1, O = 16) Procedure, Pipette 25 or 20ml of BA3 into a clean conical flask. Add 3 drops of phenolphthalein indicator. Titrate the mixture with BA4 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below, Volume of pipette used...................................................................cm3 Experiment

1

2

3

4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA4 used(cm3) Values used to calculate the average volume of BA4 ..................................................................................................................................................................................................................... ........................................................... Average volume of BA4 ..................................................................................................................................................................................................................... ................................................................................................................................................................................................... Write the ionic equation for the reaction between BA3 and BA4 ..................................................................................................................................................................................................................... ........................................................... i) Calculate the molarity of BA3 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .......................................... i) Calculate the number of moles of BA3 that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... ii) Calculate the number of moles of BA4 that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .....................................................................................................................................................................................................................

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..................................................................................................................................................................................................................... ......... iii) Determine the molarity of BA4 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... iv) Calculate the relative atomic mass of X in the acid ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... Teachers comment and evaluation ........................................................................................................................................................................... ....................... ............................................................................................................ ...................................................................................... ............................................................................................................................. ...................................................................

e) Practical 5 Determination of the number of moles of water of crystallisation You are provided with the following, BA5 which is a solution containing 12.6g of dibasic acid Y.nH2O per litre of solution BA6 which is made by dissolving 8g of sodium hydroxide to make 1 litre of the solution ( 1 mole of Y reacts with 2 moles of sodium hydroxide, molar mass of Y = 90) Procedure, Pipette 25 or 20ml of BA5 into a clean conical flask. Add 3 drops of phenolphthalein indicator, then titrate with BA6 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below.

Volume of pipette used...................................................................cm 3 Experiment

1

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA6 used(cm3)

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2

3

4

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Values used to calculate the average volume of BA6 ..................................................................................................................................................................................................................... ................................. Average volume of BA6 ..................................................................................................................................................................................................................... ............................................................................................................................................................ a) Calculate, i) Molarity of sodium hydroxide. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... ii) The number of moles of sodium hydroxide that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... iii) The number of moles of Y.nH2O that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... iv) The molarity of Y.nH2O ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... v) Determine the value of n in Y.nH2O ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .........

Teachers comment and evaluation ............................................................................................................................. ..................................................................... ............................................................................................................................. ..................................................................... ............................................................................................................................. ................................................................... f) Practical 6 Determination of the stoichiometry of the reaction between the acid HnA and sodium hydroxide You are provided with the following

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 BA1 which is 0.3M sodium hydroxide solution  Ba2 which is 0.2M solution of acid HnA Procedure, pipette 25 or 20ml of BA1 into a clean conical flask. Add 2 drops of methyl orange indicator. Titrate the mixture with BA2 from the burette. Repeat the titration to obtain consistent results. Record your values in the table below, Volume of pipette used...................................................................cm 3 Experiment

1

2

3

4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA2 used(cm3) Values used to calculate the average volume of BA2 ..................................................................................................................................................................................................................... ....................................................................... Average volume of BA2 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ... a) Calculate the, i) Number of moles of sodium hydroxide that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ...... ii) The number of moles of HnA that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ...... b) Determine the mole ratio of the acid HnA to sodium hydroxide. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .........

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c) The value of n in HnA ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... Write the equation for the reaction. ..................................................................................................................................................................................................................... ...........................................................

Teachers comment and evaluation ............................................................................................................................. ..................................................................... ........................................................................................................................................................................................... ....... ............................................................................................................................ ....................................................................

g) Practical 7 Determining the basicity of an acid HnX You are provided with the following  BA1 which is 0.2 moles per litre of HnX  BA2 which is 0.5M solution of sodium hydroxide. You are required to determine the basicity, n of the acid Procedure, Pipette 25 or 20ml of BA2 into a clean conical flask. Add 3 drops of methyl orange indicator. Titrate the mixture with BA1 from the burette. Repeat the procedure to obtain consistent titres. Record the results in the table below, Volume of pipette used...................................................................cm 3 Experiment

1

2

3

4

Final burette reading (cm3) Initial burette reading (cm3) Volume of BA1 used(cm3) Valuesused to calculate the average volume of BA1 ..................................................................................................................................................................................................................... ........................................................ Average volume of BA1 ..................................................................................................................................................................................................................... ................................................................................................................................................................................................... a) Calculate the, I. Number of moles of sodium hydroxide that reacted

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..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... II. The number of moles of HnX that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... III. Determine the mole ratio of the acid HnX to sodium hydroxide ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... IV. The basicity, n of the acid HnX ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ......... Write an ionic equation of the reaction between the acid and base (sodium hydroxide) ..................................................................................................................................................................................................................... ..................... Teachers comment and evaluation ...................................................................................................................................................................... ............................ ....................................................................................................... ........................................................................................... ............................................................................................................................. ...................................................................

2.

QUALITATIVE ANALYSIS

This section forms question number two of chemistry paper 545/3 or paper 545/4. It is mainly based on the chemistry of salts which is learnt in senior two. Students are therefore advised to revise the chemistry of salts in order to present quality work in this section. Safety is the most important aspect for students of chemistry in the laboratory; therefore students should take caution and responsibility. Students should revise all rules and regulations of the laboratory before performing practical. Qualitative analysis requires a student to carry out a number of sample tests on one or more substances mixed, the observation a recorded from which deduction about the substance are made. The common apparatus used in this case include,  Test tube rack, test tubes, boiling tubes, spatula, Bunsen burner, test tube holder, glass rod, filter paper, filter funnel, wash bottle, a set of reagent bottles

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The assessment in this section is based on the quality of the information provided by the student. The following points should be noted while making a practical report in this section.    

Make clear and true observations Precisely write observation Make your deductions logically from the observation A wrong observation cannot lead to a correct deduction. Qualitative analysis at this level mainly deals with the chemistry of few selected non-transitional metals cations and some transitional metal cations and some anions.

a) Non- transition cations Salts of non-transition metals are usually white or colourless and the generally dissolves in water or dilute acids to form colourless solutions. Cations considered in this case are, o Zinc ions, Zn2+ o Lead ions, Pb2+ o Aluminium ions, Al3+ o Calcium ions, Ca2+ o Magnesium ions, Mg2+ o Barium ions, Ba2+ o Ammonium ions, NH4+ b) Transition metal cations Salts of transition metals exhibit characteristic colours and they usually dissolves in water or dilute acids to form coloured solutions. The cations considered in this case include, o Copper (II) ions, Cu2+ o Iron (II) ions, Fe2+ o Iron (III) ions, Fe3+ c) o o o o o o o o

Anions considered at this level include, Carbonate ions, CO32Sulphate ions, SO42Chloride ions, ClNitrate ions, NO3Sulphite ions, SO32Others include, Bromide ions, BrIodide ions, INitrite ions, NO2 PRELIMINARY TESTS

a) Appearance, Note the physical properties of the substance provided, the physical properties considered at this level include colour, texture, smell etc. Physical properties give crucial information about the presence of particular ions. This is possible because ions/cations or anions have unique physical properties, as shown in table below.

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Observation

deduction

White solid (crystalline or pawderly), if crystalline it may be a hydrated salt

Non-transition metal cations present

Blue crystals

Cu2+ ions present

Green solid

Fe2+ ions present

Brown/yellow solid

Fe3+ ions present

Therefore Ca2+, Mg2+, Ba2+, Al3+, Pb2+, Zn2+, NH4+ ions probably present.

b) Action of heat, Heat two spatula endful of the substance in a dry hard glass tube initially slowly and then strongly until there is no further change. Identify the gases evolved, their smell, colour, action on damp litmus paper, action on the splint, and usual confirmatory tests for gases. Observe the residue when hot and when cold. Consider the table below, Observation Deduction Water of crystallisation Colourless liquid condenses on sides of ∴ Hydrated salt, HCO3-, HSO4-, OHboiling tube, liquid turns anhydrous probably present copper (II) sulphate from white to blue. Or turns cobalt (II) chloride from blue to pink. NH3 gas evolved, White sublimate, colourless gas with ∴ NH4+ ions present pungent smell, gas turns damp red litmus paper blue, gas forms dense white fumes with conc.HCl CO2 gas evolved Colourless gas evolved, gas turns moist ∴ CO32-, HCO3- probably present blue litmus paper red, gas turns lime water milky O2 gas evolved Colourless gas liberated, gas is neutral to ∴ NO3- probably present litmus paper, gas relights a glowing splint. Mixture of NO2 and O2 gases evolved. Cracking noise, brown fumes of a gas ∴ NO3- present. evolved, gas has irritating smell, gas turns damp blue litmus paper red, gas relights a glowing splint. Cl2 gas given off Pale yellow fumes of gas evolved, gas turns ∴ Cl- probably present moist blue litmus paper red and bleaches, gas turns KI solution from colourless to brown. Note. Most chlorides usually impart the characteristic colour of the metal in the Bunsen flame. The pale yellow colour may not be observed HCl gas evolved Misty white fumes of a gas, gas has ∴ Cl- present

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

pungent irritating smell, gas turns moist blue litmus paper red, gas forms dense white fumes with ammonia This is also true for chlorides, here the chlorides should be heated with conc. Acid Colourless gas evolved, gas has irritating smell, gas turns moist blue litmus paper red and bleaches it, gas turns purple acidified potassium permanganate colourless and turns acidified dichromate solution from orange to green White fumes with irritating smell, turns moist blue litmus paper red, turns barium nitrate milky.

SO2 gas evolved ∴ SO42- probably present

SO3 gas given off ∴ SO42-, HSO4- probably present.

Colour of the residue

Observation Residue is yellow hot, white cold

Deduction Residue is ZnO ∴ Zn2+ present

Residue is brown hot, yellow cold

Residue is PbO ∴ Pb2+ present

Residue turns from black to brown

Fe2O3 is formed ∴ Fe2+ present

Residue is black hot, black cold

Residue is CuO ∴ Cu2+ present

c) Solubility test. The solvent used to dissolve solutes is water. For practical work, distilled water should be used for making solutions for qualitative analysis. Here the knowledge of solubility of salts is crucial. Consider the summary of the solubilities of common salts in water in the table below. Salt Carbonates Chlorides

Solubility All are insoluble except potassium, sodium, and ammonium carbonates All are soluble except silver and lead chlorides. Lead

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

chloride is soluble in hot water. Nitrates Sulphates

All are soluble All are soluble except barium and lead sulphates, calcium sulphate is only sparingly soluble.

Note.  If a salt is soluble, state the colour of the solution formed.  For a mixture of salts where one is soluble and the other is insoluble, you will be required to filter. In this case, describe the colour of the residue and the filtrate.  Where you are require to wash the residue, do it at least two times to ensure that the particles of the soluble salt are dissolved. Allow to settle and decant the solution before you analyse the residue as required.  Where the salt is insoluble in water, you will be required to dissolve in cold dilute acids or warm dilute acid. To a spatula endfull of the substance in the test tube add dilute nitric acid or hydrochloric acid or sulphuric acid.  When effervescence occurs, identify the gas evolved by their common tests as described before. Note the colour of the resultant solution. Colour of the solutions Observation Dissolves to form a colourless solution Dissolves to form a blue solution Dissolves to form a green solution Dissolves to form a brown solution, the solution turns blue litmus paper red

Deduction Non-transitional metal cations ie Mg2+, Ca2+, Ba2+, Al3+, Pb2+, Zn2+, NH4+ probably present. Cu2+ present Fe2+ present Fe3+ present

IDENTIFICATION OF CATIONS There are two categories of cations considered here, these are 1) Non-transition metal cations, these are non-coloured and their solutions are colourless. They include Ca2+, Mg2+, Ba2+, Al3+, Pb2+, Zn2+or NH4+ ions 2) Transition metal cations, these are coloured and their solutions are also coloured. Refer to colour of the solutions described before. These include Cu2+, Fe2+, Fe3+ which are blue, green, and brown respectively. The above cations are identified by treating the solutions separately with sodium hydroxide solution and ammonia solution. These alkali precipitate insoluble hydroxides.



Activity You are provided with the following, Solutions containing Mg2+, Ca2+, Ba2+, Al3+, Pb2+, Zn2+, NH4+, Cu2+, Fe2+, Fe3+ ions

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  

Test tubes 2M sodium hydroxide solution 2M ammonium solution Procedure,  To 2cm3 of each of the solutions in a separate test tubes, add sodium hydroxide solution drop wise until excess. Record your observations in the table 1 below  Repeat the procedure with 2M ammonia solution and record your observation in table 2 Effect of sodium hydroxide Table 1

cations Ca2+ Mg2+ Ba2+ Al3+ Pb2+ Zn2+ NH4+ Cu2+ Fe2+ Fe3+

Observation

Effect of ammonia solution Table 2 cations Ca2+ Mg2+ Ba2+ Al3+ Pb2+ Zn2+ NH4+ Cu2+ Fe2+ Fe3+

Observation

Questions, 1. List the ions that form white ppt with sodium hydroxide.

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..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. 2. List the ions that form white ppt with sodium hydroxide insoluble in excess. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. 3. List the ions that form white ppt with sodium hydroxide soluble in excess. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. 4. Which ions form coloured ppt with sodium hydroxide insoluble in excess, state the respective colours of the ions.

5.

6.

7.

8.

9.

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. Which ions form coloured ppt with sodium hydroxide soluble in excess, specify respective colours of the ions for both ppt and solutions. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. List the ions that form white ppt with ammonium hydroxide. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. List the ions that form white ppt with ammonium hydroxide insoluble in excess. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. List the ions that form white ppt with ammonium hydroxide soluble in excess. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. Which ions form coloured ppt with ammonium hydroxide insoluble in excess, state the respective colours of the ions.

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................. 10. Which ions form coloured ppt with ammonium hydroxide soluble in excess, specify respective colours of the ions for both ppt and solutions. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

b) Compare the observations with sodium hydroxide and ammonia solutions, show differences and similarities. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .......... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ...........

Now compare your results with the tables below, Effect of sodium hydroxide Cations Observation 2+ Ca White ppt, insoluble in excess sodium hydroxide Mg2+ Ba2+ Al3+ Pb2+ Zn2+ NH4+ Cu2+ Fe2+ Fe3+

White ppt, insoluble in excess sodium hydroxide White ppt, insoluble in excess sodium hydroxide White ppt, soluble in excess, forming a colourless solution White ppt, soluble in excess, forming a colourless solution White ppt, soluble in excess, forming a colourless solution Solution remains colourless, colourless gas evolved, gas turns moist red litmus paper blue, gas forms dense white fumes with conc. HCl Blue ppt, insoluble in excess sodium hydroxide Green ppt, insoluble in excess, turns brown on standing Brown ppt, insoluble in excess sodium hydroxide Effect of ammonia solution

Cations Ca2+ Mg2+ Ba2+ Al3+ Pb2+ Zn2+ NH4+ Cu2+ Fe2+

Observation White ppt, soluble in excess, forming a colourless solution White ppt, insoluble in excess ammonium hydroxide White ppt, insoluble in excess ammonium hydroxide White ppt, insoluble in excess ammonium hydroxide solution White ppt, insoluble in excess ammonium hydroxide White ppt, soluble in excess, forming a colourless solution No observable change, solution remains colourless. Blue ppt, soluble in excess, forming a deep blue solution Green ppt, insoluble in excess, turns brown on standing

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Fe3+

Brown ppt, insoluble in excess sodium hydroxide

Note  

NH4+, K+ and Na+ ions do not form precipitates with both sodium hydroxide and ammonia solution. When a solution containing NH4+ ions and sodium hydroxide is warmed, ammonia gas is evolved. Refer to the tests for ammonia Explanation and equations The cations of the salt solutions react with sodium hydroxide or ammonia solutions to form insoluble metal hydroxides which are observed as precipitates. The alkalis provides the hydroxide ions, OH- to the cations. Generally, Mn+ (aq) + nOH-(aq)

M(OH)n(s)

Where M is the metal, n is the valance of the metal Mg2+(aq) + 2OH-(aq)

Mg(OH)2(s) (White ppt)

Ca2+(aq) + 2OH-(aq)

Ca(OH)2(s) (White ppt)

Zn2+(aq) + 2OH-(aq)

Zn(OH)2(s) (White ppt)

Pb2+(aq) + 2OH-(aq)

Pb(OH)2(s) (White ppt)

Al3+(aq) + 3OH-(aq)

Al(OH)3(s) (White ppt)

Cu2+(aq) + 2OH-(aq)

Cu(OH)2(s) (blue ppt)

Fe2+(aq) + 2OH-(aq)

Fe(OH)2(s) (green ppt)

Fe3+(aq) + 3OH-(aq)

Fe(OH)3(s)

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

(brown ppt)

In excess sodium hydroxide, the white ppt of zinc hydroxide, lead hydroxide, aluminium hydroxide dissolves forming colourless solutions of zincate, plumbate, aluminate complex ions respectively. Zn(OH)2(s) + 2OH-(aq)

[Zn(OH)4]2-(aq) (Zincate ions)

Pb(OH)2(s) + 2OH-(aq)

[Pb(OH)4]2-(aq) (plumbate ions)

In excess ammonia solution, zinc (II) hydroxide dissolves to form colourless solution of tetra ammine Zinc (II) ions whereas copper (II) hydroxide dissolves to form a deep blue solution of tetra ammine copper (II) ions as below Zn(OH)2(s) + NH3(aq)

[Zn(NH3)4]2+(aq) + 2 OH-(aq) (tetra ammine Zinc (II) ions)

Cu(OH)2(s) + NH3(aq)

[Cu(NH3)4]2+(aq) + 2 OH-(aq) (tetra ammine copper (II) ions)

CONFIRMATORY TESTS a) Zinc (II) ions, Zn2+ To a solution of zinc ions, add ammonia solution drop wise until excess Observation, White precipitate, soluble in excess ammonia forming a colourless solution b) Lead (II) ions, Pb2+ Note, the test here can be used to distinguish Pb2+ from Al3+ ions I) Effect of dilute sulphuric acid A white ppt is formed with Pb2+ according to the equation. Pb2+(aq) + SO42-(aq) PbSO4(s) 3+ No observable change with Al , solution remains colourless II)

III)

With dilute hydrochloric acid Add few drops of dilute hydrochloric acid to the solution of suspected ions Observation, White ppt formed, soluble on warming and reappears on cooling. Pb2+(aq) + 2Cl-(aq) PbCl2(s) 3+ No observable change with Al , solution remains colourless With potassium iodide solution To a solution of suspected ions is added 3 drops of KI solution Observation, Yellow ppt is formed

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Pb2+(aq) + 2l-(aq) Pbl2(s) 3+ No observable change with Al , solution remains colourless IV)

With potassium dichromate solution To 2cm3 add 2 drops of potassium dichromate solution Observation, Yellow ppt is formed Pb2+(aq) + CrO42-(aq) PbCrO4(s) 3+ No observable change with Al , solution remains colourless

c) Copper (II) ions, Cu2+ I) potassium iodide solution To solution of unknown in test tube, add equal volume of KI Observation, White ppt formed in a brown solution (you can filter to clearly see the white ppt, or add sodium thiosulphate solution to it, the brown colour is discharged leaving the white ppt) II) potassium hexacynoferrate (II) solution To a solution of suspected ions, add 4 drops of potassium hexacynoferrate (II) solution Observation, Brown ppt is formed d) Iron (II) ions, Fe2+ To the solution of suspected ions, add 3 drops of potassium hexacynoferrate (III) solution Observation, A dark blue ppt is formed e) Iron (III) ions, Fe3+ To the solution of Fe3+ ions add potassium hexacynoferrate (II) solution Observation, Dark blue ppt is formed Or, Add Aluminium thiocyanate solution Observation, Deep red solution is formed. IDENTIFICATION OF ANIONS 1. Carbonate ions, CO32a) Effect of heat. On heating strongly, carbonates decompose producing a colourless gas, gas turns moist blue litmus paper red and lime water milky. Carbonates of group one and ammonium carbonate, MCO3(s) MO(s) + CO2(g) b) Effect of dilute acids.

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Carbonates react with dilute acids with effervescence of a colourless gas, gas turns moist blue litmus paper red and lime water milky. Solution is colourless. Generally, MCO3(s) + 2HX (aq) MX2(aq) + H2O(l) + CO2(g) c) Reaction with barium chloride or nitrate solution. Carbonates form white ppt of barium carbonate, when little of dilute acid is added; the ppt dissolves in the acid forming colourless solution. Ba2+(aq) + CO32-(aq) BaCO3(s) d) Reaction with silver nitrate solution A white ppt of silver carbonate is formed. The ppt dissolves in aqueous ammonia or dilute nitric acid forming colourless solution. Ag+(aq) + CO32-(aq) Ag2CO3(s) e) Reaction with lead nitrate or lead ethanoate solutions White ppt of lead carbonate is formed which dissolves in dilute acid forming colourless solution. Pb2+(aq) + CO32-(aq) PbCO3(s) 2. Test for chloride ions, Cla) Reaction with silver nitrate solution. To the solution of the chloride, add dilute nitric acid followed by silver nitrate solution. A white ppt is of silver chloride is formed, Ag+(aq) + Cl-(aq) AgCl(s) b) Reaction with concentrated sulphuric acid When solid chlorides are warmed with concentrated sulphuric acids, a colourless gas with irritating smell, turns moist blue litmus red and forms dense white fumes with ammonia is evolved. SO42-(aq) + Cl-(s) HSO4-(aq) + HCl(g) 3. Test for sulphate ions, SO42a) Add dilute HCl or HNO3 acid followed by barium chloride or barium nitrate respectively to a solution of SO42- ions. A white ppt is formed, insoluble in dilute HCl or HNO3 acid Ba2+(aq) + SO42-(aq) BaSO4(s) b) Add 3 drops of lead nitrate solution and warm White ppt formed Pb2+(aq) + SO42-(aq) PbSO4(s) 4. Test for sulphite ions, SO32a) Add barium chloride solution or barium nitrate solution to the solution containing suspected ions A white ppt is formed, soluble in dilute hydrochloric acid or nitric acid forming a colourless solution. Ba2+(aq) + SO32-(aq) BaSO3(s) + BaSO3(s) + 2H (aq) Ba2+(aq) + SO2(g) + H2O(l)

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b) Add lead nitrate solution to the solution of suspected ions A white ppt is formed which dissolves in dilute nitric acid forming a colourless solution. Pb2+(aq) + SO32-(aq) PbSO3(s) PbSO3(s) + 2H+(aq) Pb2+(aq) + SO2(g) + H2O(l) 5. Test for nitrates Add an equal volume of freshly prepared iron (II) sulphate solution to the suspected solution of the nitrate, tilt the test tube as shown in the figure below, then add conc. Sulphuric acid to the mixture along the sides of the test tube. Diagram

Observation, A brown ring is formed between the two layers of solutions Explanation, Conc. Sulphuric acid is denser than the layer containing the suspected nitrate ion and iron (II) sulphate solution. Conc. Sulphuric acid reacts with the nitrate to produce nitric acid. The nitric acid is reduced to nitrogen (II) oxide by iron (II) sulphate. The nitrogen (II) oxide formed reacts with unreacted iron (II) sulphate to form a brown nitroso-iron (II) sulphate which appears as a brown ring FeSO4(aq) + NO(g) FeSO4.NO(aq) Note, Iron (II) sulphate is easily oxidised by oxygen from air to form iron (III) sulphate within a short time, which is why freshly prepared iron (II) sulphate is used.

Example 1 You are provided with substance Z which contains one cation and two anions. Carry out the following tests to identify the cation and anions in Z. Identify any gases evolved. Test Heat a spatula end-full of Z in a dry test tube until there is no further change

Observation A colourless gas evolved, gas turns moist blue litmus paper red, gas turns lime water milky Residue is yellow hot, white cold

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Deduction Gas is CO2 Hence CO32-, HCO3-, present Residue is ZnO Hence Zn2+ present

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Dissolve two spatula end-full of Z in distilled water, filter and keep both the filtrate and residue. Divide the filtrate into four equal portions, To the first portion, add sodium hydroxide solution drop wise until excess To the second portion, add ammonia solution drop wise until excess To the third portion, add 3 drops of lead nitrate solution Carry out a test of your own to confirm the anion in Z To the fourth portion, add dilute nitric acid followed by barium nitrate solution Dissolve the residue in dilute hydrochloric acid and divide the resultant solution into two equal portions. To the first portion, add sodium hydroxide solution drop wise until excess To the second portion, add ammonia solution drop wise until excess

Partially dissolves forming a colourless solution and white residue White ppt, dissolves in excess forming a colourless solution

Zn2+, Pb2+, Al3+,Ba2+, Mg2+, Ca2+ probably present Zn2+, Pb2+, Al3+, probably present

White ppt, soluble in excess forming a colourless soltion

Zn2+ confirmed present

White ppt formed

SO42-, Cl- probably present

White ppt formed

SO42- confirmed present

Dissolves with effervescence evolving a colourless gas, gas turns moist blue litmus paper red, gas turns lime water milky A colourless solution formed white ppt formed

Gas is CO2 Hence CO32- confirmed present

White ppt, soluble in excess ammonia solution forming a colourless solution

Zn2+ confirmed present

Zn2+, Pb2+, Al3+, probably present

Identify the (i) cation in Z Zn2+ (ii) anions in Z CO32-, SO42PRACTICAL SHEDULES a) Practical 1 You are provided with substance H which contains one cation and one anion. Carry out the following tests to identify the cation and anion in H. Identify any gases evolved. Test Appearance of H Heat a spatula end-full of H in a dry boiling tube until there is no further change Dissolve two spatula end-full of H in 5ml of distilled water. Divide the solution in four

observation

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

equal portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add ammonia solution drop wise until excess to the third portion , add 3 drops of lead nitrate solution Use the fourth portion to carry out a test of your own to conform the anion in H

Identify the : Cation in H....................................................... Anion in H.......................................................

b) Practical 2 You are provided with substance P which contains two cations and one anion. Carry out the following tests to identify the ions in P. Identify any gases evolved. Test Appearance of P Heat a spatula end-full of P in a dry boiling tube until there is no further change Dissolve two spatula end-full of H in 5ml of distilled water. Filter and keep both the residue filtrate. Divide the solution in four equal portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add ammonia solution drop wise until excess to the third portion ,

observation

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

add 3 drops of lead nitrate solution Use the fourth portion to carry out a test of your own to conform the anion in P Dissolve the residue in dilute sulphuric acid and warm. Divide the resultant solution in two equal portions. To the first portion, add sodium hydroxide solution drop wise until excess To the second portion, add ammonia solution drop wise until excess Identify the : Cations in P....................................................... Anion in P..........................................................

c) Practical 3 You are provided with substance X which contains one cation and two anions. Carry out the following tests to identify the ions in X. Identify any gases evolved.

Test Heat a spatula end-full of X in a dry boiling tube until there is no further change

observation

Dissolve two spatula end-full of H in 5ml of distilled water. Filter and keep both the residue filtrate. Divide the solution in four equal portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add ammonia solution drop wise until excess to the third portion , add 3 drops of lead ethanoate solution Use the fourth, add dilute hydrochloric acid followed by barium chloride solution Dissolve the residue in dilute nitric acid and warm. Divide the resultant solution in two equal portions. To the first portion, add sodium hydroxide solution drop wise until excess To the second portion, add ammonia solution drop

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

wise until excess Identify the : Cation in X....................................................... Anions in X........................................................ d) Practical 4 You are provided with substance Q which contains two cations and one anion. Carry out the following tests to identify the ions in Q. Identify any gases evolved.

Test Heat a spatula end-full of Q in a dry boiling tube until there is no further change

observation

Dissolve two spatula end-full of H in 5ml of distilled water. To the resultant solution, add sodium hydroxide drop wise until excess. Filter and keep both the residue and filtrate Add dilute nitric acid to the filtrate until the solution becomes acidic. Divide the resultant solution into three equal portions To the second portion, add sodium hydroxide solution drop wise until excess to the third portion , add 3 drops of lead nitrate solution Use the fourth, add dilute hydrochloric acid followed by barium chloride solution Dissolve the residue in dilute nitric acid and warm. Divide the resultant solution in three equal portions. To the first portion, add sodium hydroxide

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

solution drop wise until excess To the second portion, add ammonia solution drop wise until excess Use the third portion to confirm one of the cations in Q Identify the : Cations in Q....................................................... Anion in Q..........................................................

e) Practical 5 You are provided with substance Z which contains one cation and two anions. Carry out the following tests to identify the ions in Z. Identify any gases evolved.

Test Heat a spatula end-full of Z in a dry boiling tube gently and later strongly until there is no further change Dissolve two spatula end-full of Z in 4ml of distilled water. Divide the solution into five equal portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add ammonia solution drop wise until excess to the third portion , add 3 drops of potassium iodide Use the fourth, add 3 drops lead nitrate solution To the fifth portion, carry out a test of your choice to confirm the anion in Z

observation

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Identify the : Cations in X....................................................... Anion in X........................................................ f) Practical 6 You are provided with substance T which contains two cations and two anions. Carry out the following tests to identify the ions in T. Identify any gases evolved.

Test Heat a spatula end-full of T in a dry boiling tube until there is no further change Dissolve two spatula end-full of T in 5ml of distilled water. Then add 4 drops of sodium carbonate solution. Filter and keep both the residue filtrate. Divide the solution in three equal portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add 3 drops of lead nitrate solution Use the third portion , carry out a test of your own to confirm the anion in T Use the fourth, add dilute hydrochloric acid followed by barium chloride solution Wash the residue with distilled water and dissolve in dilute nitric acid until it dissolves, divide the resultant solution in three equal portions. To the first portion, add sodium hydroxide solution drop wise until excess

observation

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

To the second portion, add potassium iodide solution To the third portion, add aqueous ammonia solution drop wise until excess Identify the : Cations in T....................................................... Anions in T........................................................

g) Practical 7 You are provided with substance Y which contains three cations and one anion. Carry out the following tests to identify the ions in Y. Identify any gases evolved.

Test Heat a spatula end-full of Y in a dry boiling tube until there is no further change Dissolve two spatula end-full of T in 5ml of distilled water. To about 1ml of the solution, add three drops of lead nitrate solution Use 1ml of the solution to carry out a test of your own to identify the cation in Y To the rest of the solution, in b) add sodium hydroxide solution drop wise until no further change. Filter and keep both the filtrate and residue Add dilute HCl acid drop wise to the filtrate until it is just acidic and divide the resultant solution into three portions To the first portion, add sodium hydroxide drop wise until excess

observation

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Deduction

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

To the second portion, add ammonium hydroxide solution drop wise until excess To the second portion, add 3 drops potassium iodide solution Dissolve the residue from c) in dilute HCl and dive the resultant solution into two portions To the first portion, add sodium hydroxide drop wise until excess To the second portion, add ammonia solution drop wise until excess Identify the : Cations in Y....................................................... Anion in Y.......................................................... CHEMICAL KINETICS Rate of reaction some reactions take place almost instantaneously like explosion of hydrogen in air mixture when lighted splint is inserted in it , a concept described as burning with pop sound. Other reactions are slow e.g rusting of iron in which a noticeable change is observed after appreciable time. Some reactions show changes in colours of reactants or of products with time. For example nitrogen oxide reacts with oxygen to form nitrogen dioxide which is brown. The gradual change in colour can be measured with time, and this can indicate rate of reaction. The change in concentration with time can be followed by titration, you will also deal with reactions in which colourless gases are evolved. During a chemical reaction, the concentration of products increases whereas that of reactants decreases. The change in concentration with time is what is termed as rate of reaction. Therefore rate of reaction is the measure of the change in quantity of reactants or products with time. Rate of reaction is precisely defined as speed/rate at which reactants are turned into products In determining the rate of a chemical reaction, the amount of product formed in a given period of time or the amount of reactants consumed in a given period of time is measured. Then the rate is expressed as amount of products formed per unit time or the amount of reactants consumed per unit time. amount of products formed Time amount of reactants consumed = Time

Rate = Rate

Rate of reaction in terms of amount of products

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

The amount of products formed can be determined by measuring the volume of gaseous products which is a measure of concentration of the products Rate =

   

amount of products formed Time

At A, the reaction has not yet started and there is no product formed Along AB, the volume of the product formed increases with time At B, the reaction is complete i.e one or both of the reactants are used up and therefore the amount of products formed remains constant. Along BC the rate of reaction is constant Using the graph above, the rate of reaction at a particular time is obtained by the drawing tangent at that time and the calculating the slope of the tangent as shown below

change in Y axis

The slope of the tangent = change in X axis =

y2 – y1 𝑋2−𝑋1

The slope of the graph gives the rate of reaction measured in respective units per unit time. Time is can be in seconds, minutes, hours or days but it is usually measured in seconds.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Rate of reaction in terms of amount of reactants consumed The amount of reactants decrease with time, consider the graph below

   

Point, P corresponds to the initial amount of the reactant before the reaction starts. Along PQ, the amount of the reactants decrease with time At Q one or both of the reactants is (are) used up and the reaction is complete. Rate of reaction is constant along QR To estimate the rate of reaction at a particular time, a tangent is drawn at that time and the slope is calculated. The slope is equal to the rate of reaction as shown below.

Slope =

change in Y change in X

Note 1  A graph should have a title  Both axes of the graph should be labelled with the quantities and their right corresponding units  A graph should have both horizontal and vertical scales  A curve should be smooth, avoid tracing points Note 2  The steeper the curve, the higher the rate of reaction  The curve becomes flat when the reaction has stopped. Therefore from the curves, it is seen that the reaction at a lower concentration goes for a long time before it ceases.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

 It is seen that when same quantities of the reactants are use in two or more cases, approximately the same amount of products are formed.

Activities for students I)

a. b.

c.

d.

e.

f.

Activity 1 10cm length of magnesium ribbon was cleaned with sand paper. 50cm3 of 0.1M dilute hydrochloric acid was measured into a clean conical flask and corked. A rubber cork was then removed and 10cm magnesium ribbon added, the stop watch was started and flask corked immediately. The set up was organised as shown below and gas evolved measured in the syringe in intervals of 5 seconds. The date was obtained and tabulated, use the values to answer questions.

Time (s) Volume of gas evolved (cm3) 0 0 5 20 10 40 15 60 20 75 25 85 30 85 35 85 40 85 45 85 Plot a graph of volume of gas evolved against time. Use your graph to find the rate of reaction at 13 seconds ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................ What volume of the gas is evolved at 16 seconds ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ...................................................................................................................................... Describe the graph you have drawn in a. above ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................................................................................... Explain precisely the shape of the graph. ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................ Write a balanced equation for the reaction

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

............................................................................................................................................................................................................... ...................................................................

II)

Activity 2 50cm3 of hydrochloric acid was measured into the conical flask. The flask and its contents were placed on a direct weighing balance. Drop of magnesium ribbon was added to acid in flask and the timer started. Mass of the flask and its contents was taken in intervals of 5 seconds until all the magnesium ribbon was reacted. The values were tabulated; use the table below to answer questions.

Time (s) 0 5 10 15 20 25 30 35 40

Mass of flask + its contents 65.50 65.45 65.35 65.30 65.27 65.25 65.25 65.25 65.25

g. Plot a graph of volume of gas evolved against time. h. Use your graph to find the rate of reaction at 17 seconds ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................ i. What is the mass of flask and contents at 13 seconds ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ...................................................................................................................................... j. Describe the graph you have drawn in a. above ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................................................................................... k. Explain precisely the shape of the graph. ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ............................................................................................................................................................................................................... ................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

l.

Write a balanced equation for the reaction ............................................................................................................................................................................................................... ................................................................... FACTORS THAT AFFECT THE RATE OF REACTION The major factors that affect the rate of reaction include temperature, concentration, surface area, pressure, light and catalyst. We shall pick temperature, surface area and concentration for practical purposes, however others can be taught in theory. a) Effect of temperature on the rate of reaction. The rate of reaction increases with increase in temperature. Increase in temperature increases the molecular velocities of which subsequently increase the kinetic energy of reacting particles. This increases frequency of interaction/collision of the reacting molecules to form products. Note. For reaction to take place, particles must collide with sufficient kinetic energy. When the temperature is increased, particles gain energy and interact with sufficient average minimum energies. This implies that activation energy of the reaction increases and so is the rate of reaction. Activation energy is the energy barrier which must be overcome by the reacting species before the reaction can proceed Practical a  You are provided with the following,  BA1 which is 1M hydrochloric acid  Solid X which is an element picked from group two.  A conical flask  Stop clock  Thermometer  Measuring cylinder  Weighing scale  You are required to determine the rate of reaction when X reacts with BA1 Procedure  Place 50ml of BA1 into a clean conical flask and record its temperature  Weigh 0.5g of X and add to BA1 in the conical flask and immediately start the stop clock  When solid X has dissolved (when effervescence stops) immediately stop the stop clock and record the time taken for X to dissolve  Repeat the above procedures but this time first heat BA1 to a temperature of 30oC before adding solid X  Repeat the experiment by first heating BA1 to temperature of 40o,50o, 60oC before adding solid X. Record your values in the table below including values for 1⁄t Exp no. 1 2 3

Vol of BA1 (cm3) 50 50 50

Mass of X (g) Room temp 30 40

Temperature of BA1 (oC)

41 MUDUKU IVAN (Bsci.Ed MUK)

Time (s)

𝟏⁄ (s-1) 𝐭

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

4 5

50 50

50 60

Questions a) State what is observed when X is added to BA1 ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... .............................................................................................................................................................................. b) Write the equation for the reaction that occur between X and BA1 ....................................................................................................................................................................................................... ....................................................................................... c) Plot a graph of i. Time against temperature 1⁄ against temperature ii. t iii. Explain the shapes of the graphs ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ...................................................................................................................... d) What is your conclusion about the two graphs you have drawn in c i) and ii) above ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ..............................................................................................................................................................................

      

    

Practical b You are provide with the following, BA1 which is 0.16M sodium thiosulphate solution BA2 which is 2M hydrochloric acid solution 2 conical flasks 2 measuring cylinders Stop clock A sheet of white paper You are required to determine the rate of reaction when a thiosulphate reacts with dilute hydrochloric acid. Procedure Using a clean measuring cylinder, transfer 50ml of BA1 into a clean conical flask. Measure and record its temperature (room temperature) Using a black or blue pen, mark a cross on the sheet of white paper. Add 5ml of BA2 into a flask and at the same time start the stop clock, swirl the mixture and place on the sheet of white paper with the cross in the middle Look down through the mixture at the cross and stop the clock when the cross just disappears. Record the time taken for the cross to just disappear in the middle. Measure another 50ml of BA1 into a clean conical flask, this time heat the BA1 to a temperature of 30oC. Add 5ml of BA2 and immediately start the stop clock, swirl the mixture and place it on a sheet of white paper with the cross in the middle. Note and record the time it takes for the cross to disappear.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

 Repeat the previous procedure but this time heat BA1 to 40oC, 50oC, 60oC respectively before adding BA2. Record your results in the table below.

Temp (oC)

Time (s)

𝟏⁄ (s-1) 𝐭

Room temp 30 40 50 60

Questions a) Plot a graph of I) Time against temperature 1⁄ against temperature II) t b) From your graph in a) I) determine the rate of the reaction at 20 seconds ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ...................................................................................................................... c) Explain the shapes of your graphs ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ...................................................................................................................... d) What is your conclusion from the two graphs ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... .............................................................. e) State and explain how the rate of reaction varies with temperature drawn in a) II) above ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... ....................................................................................................................................................................................................... .............................................................. f) Write a balanced ionic equation for the reaction that occurred between BA1 and BA2 ....................................................................................................................................................................................................... .......................................................................................

b) Effect of concentration on the rate of reaction

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

The rate of reaction increases with the increase in concentration of the reactant species. When concentration of reactants increase in a given volume of the reaction vessel, the chances of collision of reacting particles consequently increase resulting into increased reaction rate. The greater the concentration of reactants, the greater the number of interactions between reacting particles, therefore more effective collisions occur with minimum activation energy hence faster rate of reaction. However the reverse is true for concentration of products Activity 3 10cm length of magnesium ribbon was cleaned with sand paper. 50cm3 of 0.1M dilute hydrochloric acid was measured into a clean conical flask and corked. A rubber cork was then removed and 10cm magnesium ribbon added, the stop watch was started and flask corked immediately. The set up was organised as shown below and gas evolved measured in the syringe in intervals of 5 seconds. The above procedure was repeated using 0.2M hydrochloric acid. The date was obtained and tabulated, use the values to answer questions. Time (s) 0 120 240 360 480 600 720 840

Vol of gas evolved using 0.1M HCl 0.0 6.5 13.0 20.0 24.5 27.0 29.5 32.0

Vol of gas evolved using 0.3M HCl 0.0 10.0 20.0 25.5 29.5 32.0 32.0 32.0

Questions a) Plot on the same axes the volume of gas liberated using 0.1M and 0.3M HCl acid against time b) What do you notice about the graphs ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................ c) Explain the shapes of the graphs ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................. d) Find the rate of reaction for both curves at 410 seconds ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................. e) Comment on the values obtained in d) above

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................

Reaction sodium thiosulphate and dilute hydrochloric acid Sodium thiosulphate reacts with dilute hydrochloric acid to form a white/yellow precipitate of sulphur according to the following equation. Na2S2O3(aq) + 2HCl(aq) NaCl(aq) + S(s) + SO2(g) H2O(l) The ionic equation is, S2O32-(aq) + 2H+(aq) S(s) + SO2(g) H2O(l) The effect of changing concentration of thiosulphate on the rate of reaction by carrying out separate experiments in which the concentration of hydrogen ions (acid) is maintained constant and concentration of thiosulphate is varied. In separate experiments, the volume of the solution is kept constant. The beaker of the same size is used to mix the solutions and the beaker is placed on top of a sheet of paper marked with a black cross. Looking from above, the black cross disappears after precipitation of a specific amount of sulphur. In separate experiments the extent of reaction when the cross disappears will be the same but the time for the cross to disappear will inversely depend on the concentration of thiosulphate ions. Consequently the reciprocal of the time for the cross to disappear in each experiment measures the average rate of formation of the precipitate quantity per second. A graph of concentration of sodium thiosulphate against time begins with a steep slope which gradually becomes less steep before finally flattening out towards the horizontal axis. The gradient of the curve at any point measures the rate of reaction at the time represented by the point on the graph. The shape of the graph shows that the rate of reaction decreases as the concentration of sodium thiosulphate decreases. A graph of sodium thiosulphate against1⁄𝑡 , is a straight line within the limits of experimental errors. The reciprocal of the time is the measure of rate of reaction for the appropriate concentration. At a fixed temperature, the rate of reaction is directly proportional to the concentration of sodium thiosulphate solution provided that enough acid is used to react with the thiosulphate. The effect of temperature on the rate of reaction between sodium thiosulphate and dilute hydrochloric acid can be performed by heating the solution to certain temperature before adding the acid. A graph of 1⁄ against temperature can be plotted. The results from such an experiment will show that the higher 𝑡 the temperature, the greater the rate of reaction. A fairly small rise in temperature has a large influence on the rate of reaction.

Practical c You are provided with the following,  BA1 which is a solution containing 0.2M thiosulphate ions  BA2 which is a solution containing 2M hydrochloric acid  Distilled water  2 conical flasks  2 measuring cylinders  Stop clock  Sheet of white paper

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

You are required to determine the rate of reaction between thiosulphate and hydrochloric acid Procedure i. Make a cross with a blue or black pen on the sheet of white paper provided ii. Using a measuring cylinder, measure 60ml of BA1 into a conical flask iii. Add 10ml of BA2 into the BA1 in the conical flask and immediately start the stop clock iv. Swirl the mixture to mix the two solutions and place it on the cross v. Look through the solution mixture from above, record the time taken for the cross to just disappear vi. Into another clean conical flask, measure 50ml of BA1 vii. Add 10ml of distilled water to it and swirl viii. Then add 10ml of BA2 to the solution, swirl and place it on the cross ix. Look from above, record the time taken for the cross to just disappear x. Repeat procedures (iv) – (ix) but this time measure volumes of BA1 as shown in the table below. Add a volume of distilled water to ensure that the total volume of BA1 added to the flask remains 60ml xi. Record your results in the table below Exp no.

Vol of BA1 (cm3) 1 2 3 4 5

60 50 40 30 20

Vol of warer added (cm3) 0 10 20 30 40

Vol of BA2 (cm3)

Time (s)

1⁄ (s-1) t

10 10 10 10 10

BA1 reacts with BA2 according to the following equation S2O32-(aq) + 2H+(aq)

S(s) + SO2(g) H2O(l)

Questions a)

Why does the cross disappear in the experiment?

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..........................................

b) Write the balanced equation for the reaction that took place between BA1 and BA2 ..................................................................................................................................................................................................................... ............................................................................................................................................................................................................... c) Plot a graph of I) Volume of BA1 against time, t II) Volume of BA1 against 1⁄t

d) How does the concentration of BA1 affect the time for the cross to disappear ..................................................................................................................................................................................................................... .....................................................................................................................................................................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ..................... e) Determine the rate of reaction between BA1 and BA2 and state the units. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ...................................................................................................................................

THERMO-CHEMISTRY When reactions take place, bonds are either formed or broken. As a result there is a change in temperature, chemical reactions result into energy changes. The heat change that occur s during a chemical reaction referred to as a enthalpy, ∆𝐻 There are two types of reactions classified depending on heat change accompanying the reaction. These are endothermic reactions and exothermic reactions a) Endothermic reactions These are reactions which occur with absorption of heat from the surrounding. In these reactions, energy must be supplied for the reactants to be converted to products. The energy (temperature) of the products falls below that of initial energy (temperature). The enthalpy change is positive implying that energy (heat) is absorbed from the surrounding e.g when sodium thiosulphate dissolves in water. Na2S2O3(s) + (aq) Na2S2O3(aq) , ∆𝐻 = +ve b) Exothermic reactions These are reactions which occur with evolution/liberation of heat to the surrounding. The temperature (heat) rises above the initial temperature (heat). The enthalpy change accompanying the reaction is negative. This implies that heat is given out to the surrounding e.g C(s) + O2(g) CO2(g) ∆𝐻 = -ve, ∆𝐻 = -393Kjmol-393Kjmol- implies that 393Kj of energy is liberated when 1 mole of carbon is completely burnt in oxygen to form carbon dioxide Examples of heat changes  Enthalpy of neutralisation This is the quantity of heat evolved when one mole of hydrogen ions completely reacts with one mole of hydroxyl ions to form one mole of water H+(aq) + OH-(aq) H2O(l) ∆𝐻 = -57.3Kjmol-1 Neutralisation reaction is exothermic meaning that energy is given out. When a strong acid is neutralised with a strong alkali, the heat change is approximately 57.3Kjmol- . However when the alkali or acid is weak, the enthalpy change is less than 57.3Kjmol because heat is absorbed to dissociate the weak alkali or acid.  Enthalpy of solution Heat of solution is the quantity of heat liberated or absorbed when one mole of a substance is completely dissolved in water to form an infinitely dilute solution. The quantity of heat change depends on the amount of solvent used. NaOH(s) + (aq) Na+(aq) + OH-(aq) 

Heat of precipitation/displacement.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

This is the quantity of heat liberated when one mole of a given substance is completely displaced by another substance e.g when iron filings are added to a solution of copper (II) sulphate, a blue solution of CuSO4 turns to pale green and a brown solid is deposited at the bottom. The pale green solution is due to formation of iron (II) sulphate whereas the brown solid is due to formation of copper metal. CuSO4(aq) + Fe(s) FeSO4(aq) + Cu(s) Ionically, Cu2+(aq) + Fe(s) Fe2+(aq) + Cu(s) Note. Iron is able to displace copper from its ions because iron is higher than copper in the electrochemical series. Activity 4 a) When 25ml of 0.2M sulphuric acid was added to 100ml of 1m sodium hydroxide solution, the temperature of the resultant solution increased by 12.6oC. Write the ionic equation for the reaction that took place. ..................................................................................................................................................................................................................... ..................... Calculate the enthalpy of neutralisation sodium hydroxide (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................. Comment on the value obtained. ..................................................................................................................................................................................................................... .......................................................................................................................................... b) 50ml of 2M hydrochloric acid and 50ml of 2M sodium hydroxide both at 22oC were mixed in a plastic beaker. The mixture was stirred and maximum temperature obtained as 35oC. (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) Explain why a plastic beaker was used for mixing ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .................................................................................................................................................................................... Calculate the heat of the reaction ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................................... Explain precisely what would happen to the value of heat of reaction calculated above if 50ml of 2M ammonia solution was used instead of sodium hydroxide.

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................... Practical d You are provided with the following, M which is an acidic solution N which is an alkaline solution You are required to determine the morality of an acidic solution M Procedure a) Using a measuring cylinder, measure 110ml of M and transfer into a 250ml beaker, add 90ml of distilled water and mix. label this solution BA1 b) Transfer 190ml of N into another 250ml beaker using a measuring cylinder. Add 10ml of distilled water and mix. Label this solution BA2 c) Transfer BA1 into a burette. Run 25ml of BA1 into a plastic beaker d) Add at once 10ml of BA2 from the measuring cylinder into a plastic beaker containing 25ml of BA1. Gently stir with the thermometer and record the highest temperature attained by the mixture e) Repeat the procedures (c) and (d) using 15, 20, 25, 30, 35, 40ml of BA2 f) Record your results in the table below Volume of BA2 used (cm3) Temperature of the mixture (oC)

10 31.0

15 33.0

20 35.6

25

30

37.0

39.0

35 38.6

Questions, a) Plot a graph of temperature of the mixture against the volume of BA2 A graph of temperature of mixture against volume of BA2

49 MUDUKU IVAN (Bsci.Ed MUK)

40 38.0

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

10 Y-Values

temperature of the mixture (C)

9 8

7 6 5 4 3 2 1

0 0

10

20 30 volume of BA2 (cm)

40

50

b) From your graph, determine the maximum volume of BA2 required to react with 25ml of BA1 Therefore the maximum volume of BA2 required to react with 25ml of BA1 gives the highest temperature The maximum volume of BA2 = 30cm3 obtained from the graph c) Calculate the number of moles of alkali that reacted (morality of BA2 = 1.9M) 1000cm3 of BA2 contain 1.9 moles 1 cm3 will contain

30 cm3 will contain

𝟏.𝟗

𝒎𝒐𝒍𝒆𝒔

𝟏𝟎𝟎𝟎 𝟏.𝟗 𝑿 𝟑𝟎 𝟏𝟎𝟎𝟎

moles

Number of moles alkali= 0.057 moles d) Calculate the number of moles of the acid that reacted (ratio of acid to alkali = 1:2) Mole ratio of acid: alkali = 1:2 𝟏

Therefore number of moles of acid 𝟐 X 0.057 moles = 0.0285 moles e) Calculate the morality of the acid 25cm3 of the solution contain 0.0285 moles of acid 1cm3 of solution will contain 1000cm3 of solution contain

𝟎.𝟎𝟐𝟖𝟓 moles of the acid 𝟐𝟓 𝟎.𝟎𝟐𝟖𝟓 X 1000 moles 𝟐𝟓

= 1.14M

Practical e You are provided with the following,  Measuring cylinder

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

    

BA5 which is 2M sodium hydroxide solution BA6 which is 2M hydrochloric acid solution Plastic cup Thermometer Plastic beaker

You are required to determine the enthalpy of neutralisation of hydrochloric acid by sodium hydroxide Procedure i. Measure 50ml of BA5 into the plastic cup ii. Record the temperature t1 of the solution iii. Rinse the thermometer with distilled water iv. Measure 50ml of BA6 into the plastic beaker v. Measure and record the temperature t2 vi. Now add all the 50ml of BA6 into the alkali in the plastic cup vii. Stir the mixture carefully with the thermometer and record the highest temperature t3 Results Volume of BA5 used................................................................................................ Volume of BA6 used................................................................................................. Total volume of the mixture................................................................................. Temperature of BA5, t1........................................................................................ Temperature of BA6, t2......................................................................................... Average initial temperature................................................................................ Final temperature, t3........................................................................................... Determine the temperature change................................................................... Questions a) Write an equation for the reaction between BA5 and BA6 ..................................................................................................................................................................................................................... ............................................... b) Calculate the number of moles of sodium hydroxide that reacted. ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ........................................................................................................................................................................................... c) Calculate the heat evolved (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ........................................................................................................ d) Calculate the molar heat of neutralisation of sodium hydroxide by hydrochloric acid ..................................................................................................................................................................................................................... .....................................................................................................................................................................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ............................................................................................................................................. e) If 2M ethanoic acid was used instead of 2M HCl, what would be the heat change as compared to the value calculated above. Precisely explain your answer ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................................ Practical f You are provide with the following,  BA1 which is 2M NaOH solution  BA2 which is 2M HCl solution  Plastic cup  Burette You are required to determine the enthalpy of neutralisation of NaOH by HCl Procedure a) Pipette 25ml of BA1 into a clean plastic conical flask. Note and record the temperature t1 b) Note and record the temperature t2 of solution BA2 and put in the burette c) Add 5ml of BA2 from the burette to BA1, stir and record the maximum temperature of the mixture, t3 d) Repeat procedure (c) at 5ml interval until the total of 50ml of BA1 has been added e) Record the results in the table below Results Initial temperature of BA1, t1...................................................................... Initial temperature of BA2, t2..................................................................... Average temperature of the mixture........................................................ Volume of BA2 used (cm3) Maximum temperature, t3 Temperature change = t3 –

5

10 15

20

25

30

35

40

45

50

𝒕𝟏+𝒕𝟐 𝟐

a) plot a graph of temperature rise against the volume of BA2 added b) use your graph to determine the volume of BA2 required to neutralise BA1 from the graph ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................................................................................. c) calculate the morality of BA2 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .....................................................................................................................................................................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................... d) calculate the enthalpy of neutralisation of BA1 by BA2 (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .......................................... Practical g You are provided with following,  plastic cup  measuring cylinder  thermometer  0.5M copper (II) sulphate  Zinc pa (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3)wder You are required to determine the enthalpy of displacement of copper (II) sulphate by zinc Procedure a) Using a measuring cylinder, transfer 50ml of 0.5 M solution of copper (II) sulphate into a plastic cup. Note and record the temperature, t1 of the solution b) Add 2g of zinc powder and stir well but carefully with the thermometer. Note and record the highest temperature, t2 attained by the mixture Results Initial temperature of solution, t1........................................................ Final temperature of the mixture, t2.................................................... Temperature change, t2 – t1................................................................ Questions a) State what was observed ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .............. b) Write the equation for the reaction that took place ..................................................................................................................................................................................................................... ...... c) Calculate the number of moles of copper (II) sulphate solution ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................... d) Calculate the number of moles of zinc in 2g (Zn = 65.4)

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ................................................................................................................................... e) Calculate the number of moles of Zinc that reacted ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ........................................................................................................................... f) Calculate the heat change that occurred in the reaction. (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................ g) Calculate the enthalpy change in Kjmol-1 ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................ h) If magnesium instead of zinc was use, would the enthalpy change for the reaction be greater, less or equal to that you have calculated in (g) above. Explain your answer ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ............................................................................................................................

Practical h You are provided with the following,  Plastic beaker  Measuring cylinder  Distilled water  Thermometer  8g of X You are required to determine the enthalpy of solution of salt X Procedure a) Using a measuring cylinder, measure 90ml of distilled water into a plastic beaker b) Record the temperature of the water in the beaker for every minute for 4 minutes c) At the fourth minute, add a salt X and stir continuously to dissolve. Record the temperature every half a minute for 3 minutes d) Record your results in the table below. Results Time (min) Temp (oC)

1.0

2.0

3.0

4.0

4.5

5.0

54 MUDUKU IVAN (Bsci.Ed MUK)

5.5

6.0

6.5

7.0

7.5

CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

Questions i) Plot a graph of temperature against time j) Extrapolate the graph as shown below the find the change in temperature k) Calculate the heat of solution from the quantity of water used. (S.H.C = 4.2Kjmol-1c-1, density of solution = 1gcm-3) ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... .......................................................................................................................................... l) State whether the reaction is exothermic or endothermic, give a reason for your answer ..................................................................................................................................................................................................................... ..................................................................................................................................................................................................................... ...........................................................................................................................

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CONSULTED PRECISE ORDINARY LEVEL CHEMISTRY PRACTICAL GUIDE

56 MUDUKU IVAN (Bsci.Ed MUK)