Download - Teachers Manual

SIJIL TINGGI PERSEKOLAHAN MALAYSIA (STPM)

(MALAYSIA HIGHER SCHOOL CERTIFICATE)

Teacher’s Manual Practical Chemistry

Paper 962/3 (School-based Assessment)

2007/2008 Session

Majlis Peperiksaan Malaysia Bangunan MPM, Persiaran 1

Bandar Baru Selayang 68100 BATU CAVES

Selangor

Tel: 03-61369663 Fax: 03-61367329

© Majlis Peperiksaan Malaysia 2007

CONTENTS

Page

1.0

2.0

3.0

4.0

5.0

6.0

Introduction Administration of Practical Chemistry Assessment at School Moderation Practical Work Assessment Guide Table of Summary of Experiments Preparation of Solutions for Volumetric Analysis Experiment 1 Experiment 2 Experiment 3 Experiment 4 Experiment 5 Experiment 6 Experiment 7 Experiment 8 Experiment 9 Experiment 10 Experiment 11 Experiment 12 Experiment 13 Experiment 14 Experiment 15 Experiment 16 Experiment 17 Experiment 18 Experiment 19 Experiment 20 Appendix A - Student Record Appendix B - Experiment Report

1 1 4 5 9

12

15

17

20

23

26

28

31

34

37

40

42

45

49

51

54

57

60

63

66

69

72

73

STPM CHEMISTRY TEACHER'S MANUAL 2007/2008

1

SCHOOL-BASED ASSESSMENT OF PRACTICAL CHEMISTRY

1.0 Introduction 1.1 Some of the skills that should be developed in science subjects (e.g. handling of

apparatus, observation, interpretation of results, and planning) can only be fully acquired through practical work.

1.2 Continuous assessment of practical work at school throughout form six will

ensure that direct observations of all the desired practical skills and scientific attitudes of students can be made.

1.3 The practical science assessment is carried out at school level with the following

aims.

(a) To establish a practical work assessment system which is fair, accurate, and comprehensive

(b) To improve the practical skills and the quality of practical work of students

(c) To inculcate teamwork spirit, scientific attitudes, and critical thinking among students

2.0 Administration of Practical Chemistry Assessment at School 2.1 General information 2.1.1 The teacher in charge of the school-based assessment of Practical

Chemistry will be provided with a Teacher’s Manual which contains the details of the administration of Practical Chemistry assessment, practical work assessment guide, and description of experiments.

2.1.2 Majlis Peperiksaan Malaysia (MPM) will provide a softcopy of Student’s

Manual. The school is expected to make copies of the manual to be given to each student.

2.1.3 MPM has determined 20 experiments to be carried out by students. Of

these 20 experiments, only 15 compulsory experiments will be assessed by the teacher. (Refer to the Table of Summary of Experiments on pages 9, 10 and 11.) This assessment is expected to commence in early July 2007.

2.1.4 The teacher is expected to prepare the experiments according to this

manual. MPM should be informed of any modifications made by the teacher by using the Experiment Report form (See Appendix B on page 73). This form is to be printed from the separate file: Record and Report (Forms).

2.1.5 Experiments are to be carried out by students either individually or in

groups as recommended in the Table of Summary of Experiments. 2.1.6 The period of time for carrying out each experiment is as recommended in

the Table of Summary of Experiments.


2

2.1.7 The information on each experiment should be given to students before the experiment is carried out so that they can plan their practical work.

2.1.8 The teacher should ensure that a student has been given a chance to

acquire a particular skill before the assessment of that skill is made. For this purpose, the teacher may conduct another experiment before carrying out a compulsory experiment.

2.1.9 The assessment of practical work should be done by the teacher while an

experiment is being carried out and also based on the student’s practical work report.

2.1.10 For a student who is absent from an experiment, the teacher can fix

another date for the student to carry out the experiment. 2.1.11 Students may write their practical work report in either English or

Bahasa Malaysia. The report is to be submitted to the teacher on the same day the experiment is carried out unless otherwise stated. (Refer to the Table of Summary of Experiments.) Practical work reports which are not submitted on the day of the experiment are to be awarded ‘0’ mark.

2.1.12 Practical work reports which can be completed at home are to be submitted

to the teacher not later than 3 days from the date of the experiment. A penalty of 2 marks is to be imposed for the reports submitted late to the teacher. Practical work reports which are submitted later than 7 days from the date of the experiment are to be awarded ‘0’ mark.

2.1.13 For a student who has transferred to another school, the previous school is

to send the student’s Student Record, which is partially completed and signed by the subject teacher, to the student’s new school.

2.1.14 Practical work reports which have been submitted to the teacher can be

returned to students only after the teacher has completed assessing the reports and recording the marks of all students. The teacher should collect all the practical work reports before 15 October 2007 for the first year of the course and before 15 September 2008 for the second year.

2.1.15 A student whose Student Record has not been sent by the school to MPM

will be considered as not having carried out the practical work and not having attended paper 962/3.

2.2 Recording of assessment marks 2.2.1 Recording of the practical assessment marks of each student is to be done

by the subject teacher in two copies of Student Record. (See Appendix A on page 72.) Copies of this form are to be made from the softcopy provided in the separate file: Record and Report (Forms).


3

2.2.2 For each student, the teacher is to record the date of the experiment, the experiment number, and mark given to each of the skills for the 15 compulsory experiments in the Student Record. Marks are to be awarded in accordance with the practical work assessment guide on page 5, 6, 7, and 8.

2.2.3 Notes on the following cases should be written in the ‘Notes’ column on

the Student Record of the student involved.

(a) An experiment carried out at a later date for a student who was absent for the experiment

(b) Any penalty imposed for late submission of practical work report to the teacher

(c) A student who has not finished all the experiments allocated (The reason is to be stated.)

2.2.4 Practical assessment for the two-year course should be completed before

30 August 2008. 2.2.5 Once the practical assessment for the two-year course is completed, the

overall total mark for the 15 compulsory experiments is to be calculated and written in the ‘Overall total mark’ space on the Student Record. The full total mark for this practical assessment is 300.

2.2.6 The teacher may ask his or her students to check their Student Record to

ensure that the mark for each experiment and the overall total mark awarded are correct.

2.2.7 The subject teachers carrying out the practical assessment are required to

make a declaration that the recording of marks and the calculating of overall total mark in the Student Report are correct by putting their signatures in the space provided under “DECLARATION 1”.

2.2.8 The school principal should check and verify that the recording of marks

and the calculation of overall total mark in the Student Record are correct by putting his/her signature in the space provided under “DECLARATION 2”.

2.2.9 A copy of the completed Student Record of each student is to be sent

together with the experiment reports to MPM before 15 October 2008. The teacher should state the following in the covering letter.

(a) The total number of the Student Record for this subject being sent to MPM

(b) The names of students, if any, who have no Student Record to be submitted to MPM – the reason is to be stated. (This student will get ‘X’ grade for this paper. See 2.1.15.)

2.2.10 A copy of the Student Record of each student is to be kept by the school

until the end of May 2009. (See 3.2.4.)


4

3.0 Moderation The main purpose of moderation is to ensure that the practical assessment carried out at

school can be coordinated. 3.1 Moderation at school 3.1.1 If more than one teacher is involved in the students’ practical work

assessment for this subject, the teachers will have to come up with an agreed standardised marking scheme.

3.1.2 For the purpose of moderation at school, the teachers concerned are

required to compare the samples of students’ practical work reports for each experiment assessed by them.

3.1.3 The moderation panel at school should consist of teachers carrying out the

practical work assessment for this subject. 3.1.4 The moderation panel should be chaired by the most senior teacher for this

subject.

3.2 Interschool moderation 3.2.1 For the purpose of interschool moderation by MPM, schools are required

to submit all the assessed practical work reports of a student getting the highest overall total mark, a student getting moderate overall total mark, and a student getting the lowest overall total mark to MPM.

3.2.2 The moderation process may be carried out statistically by correlating the

students’ performance in practical work to their performance in other papers and/or through the remarking of samples of students’ practical work reports by MPM moderators.

3.2.3 In the remarking, changes to the order of positions of students which have

been decided by the teacher will only be done in extraordinary cases. If necessary, the school may be asked to submit the samples of practical work reports of other students.

3.2.4 As appeal cases for STPM examination are expected to be completed in

May 2009, students’ practical work reports should be kept by the school until the end of May 2009 before they are destroyed.


5

4.0 Practical Work Assessment Guide Students will be assessed based on the following skills: 4.1 Skill A: Use of techniques and manipulation of apparatus and materials

(9 marks) The assessment is carried out by observations for six compulsory experiments

which utilise different apparatus. Students should not know as to when and how frequent this skill is to be assessed.

Skill A is divided into three levels as follows: 4.1.1 With guidance, the student can carry out simple practical work using

common equipment and the materials provided. (3 marks) 4.1.2 Sufficient capability − in general, the student is able to use and

manipulate the apparatus to a suitable degree of accuracy. (6 marks) 4.1.3 All cognitive skills are displayed. The experiment is conducted skillfully

to a suitable degree of accuracy without assistance. (9 marks) 4.2 Skill B: Observations, measurements, and recording (6 marks) The assessment is carried out based on the practical work reports for 15

compulsory experiments which require students to fill in results or to record observations. The teacher is required to carry out each of the compulsory experiments and use his/her results or observations as standards to assess students for this skill.

The marking scheme for skill B is divided into three topics as follows: 4.2.1 Volumetric Analysis (a) Correct readings (CR) and sufficient readings (SR). (2 marks) Correct readings − both the initial and final readings are recorded in

the correct spaces and to two decimal places, except for zero. Sufficient readings − at least two volume readings within the range

of 0.10. (b) Correct average set (AS) and mean (M) (2 marks) Correct average set − correct difference between the final and initial

readings. Correct mean − arithmetic mean for titres used/obtained to two

decimals places.


6

(c) Accuracy − difference in mean value between the teacher and the student. (2 marks)

− Give TWO marks for the difference between 0.00 cm3 and

0.30 cm3. − Give ONE mark for the difference between 0.31 cm3 and

0.50 cm3. − No mark for the difference greater than 0.50 cm3. 4.2.2 Physical Quantity and Technique (Synthesis) (6 marks) (a) The table is completed with data in the correct spaces. (2 marks)

Minus ONE mark if the table is not complete. (b) All calculations of the data in the table are correct. (1 mark) (c) Appropriate decimal places. (1 mark) Example: − Temperature readings to one decimal place. (± 0.1 °C) − Weight measurements to two decimal places. (± 0.01 g) − Burette readings to two decimal places. (± 0.05 cm3) (d) Accuracy − difference of readings between the student and

the teacher. (2 marks) − difference between 0% and 10%. (2 marks) − difference > 10% to 20%. (1 mark) − difference > 20%. (0 mark) 4.2.3 Technique (Qualitative Analysis) − Filling the ‘observation’ space correctly. (6 marks) − Minus ONE mark for each incorrect observation. 4.3 Skill C: Interpretation of experimental observations and data (6 marks) The assessment is carried out based on the practical work reports for 13

compulsory experiments in which students need to answer questions and make deductions. The teacher is required to carry out each of the compulsory experiments and use his/her answers and deductions as standards to assess students for this skill.


7

The marking scheme for skill C is divided into two levels as follows: 4.3.1 Volumetric Analysis, Physical Quantities, and Technique (Synthesis) (a) Give ONE mark for each question, other than graphs, which is

correctly answered. (6 marks) Minus ONE mark for each incorrect answer. (b) Graph (2 marks) − Give ONE mark for axes labelled, and with the correct units. − Give ONE mark for the correct shape of the graph. 4.3.2 Technique (Qualitative Analysis) (a) Filling the ‘deduction’ space correctly. (5 marks) Minus ONE mark for each incorrect deduction. (b) Deducing the identity of the salt/ion correctly. (1 mark) 4.4 Skill D: Design and planning of investigation (12 marks) The assessment is carried out based on the practical work reports for four

compulsory experiments which require students to plan the experiment by themselves.

Skill D is divided into three levels as follows: 4.4.1 Neat and good planning of the experiment according to the format of

practical report which include (a) title, (b) purpose, (c) materials and apparatus, (d) theory/introduction, (e) procedure/tests (for qualitative analysis), (f) results (including calculations/observations) (for qualitative

analysis), (g) conclusion/deduction (for qualitative analysis), (h) comments (on the experiment and/or results and/or safety measures/

precautions), identification of substance, and confirmation tests (for qualitative analysis). (8 marks)


8

4.4.2 The student can complete the experiment within a specified period of time.

(2 marks) 4.4.3 General assessment by the teacher on the planning done by the student. (2 marks) 4.5 Skill E: Scientific and critical attitudes (10 marks) Overall assessment is carried out three times by observations (once after each

semester). Among the attitudes expected of a student are self-reliant, trustworthy, fair,

curious, inquisitive, having initiative, innovative, receptive to new ideas, cooperative, and caring for the environment.

Skill E is divided into three levels (once in each of the three semesters) as follows: 4.5.1 Weak − 3 marks

4.5.2 Fair − 6 marks

4.5.3 Good − 10 marks Summary of the allocation of mark and percentage for each skill

Skill Mark Percentage Notes

A

54

(6 observations × 9)

18% For 6 experiments which use

different apparatus out of 15 compulsory experiments

B

90

(15 reports × 6)

30% For 15 compulsory experiments

which require students to fill in or record results or observations

C

78

(13 reports × 6)

26% For 13 experiments which require

students to answer questions and to make deductions out of 15 compulsory experiments

D

48

(4 reports × 12)

16% For 4 compulsory experiments

which require students to plan the experiment by themselves

E

30 (3 observations × 10)

10% Overall assessment is carried out

after each semester.

Total 300 100%


9

5.0 Table of Summary of Experiments

Experiment Topic Subtopic Purpose Time Mode of working

Report to be

completed

Skills tested

1* Acid base To determine the exact concentration of a mineral acid, HXO4 and to determine the relative atomic mass of the element X

1½ hours

Individually In the laboratory

A, B, C, E

2* Redox To determine the ratio of the number of moles of hydroxyammonium ions to the number of moles of iron(III) ions participating in the reaction

1½ hours


A, B, C, E

3* Acid base and redox

To determine the mass of sodium ethanedioate used to prepare a solution containing sodium ethanedioate and hydrated ethanedioic acid

1½ hours

In groups In the laboratory

A, B, C, E

4 Purity and stoichiometry

To determine the purity of a sample of sodium sulphite crystals

1½ hours


A, B, C, E

5*

Volumetric analysis

Stoichiometry To determine the exact concentration of a monobasic acid, HX

1½ hours


A, B, D, E

6* Thermochemistry To determine the heat of neutralisation of a strong acid with a strong base

1½ hours


A, B, C, E

7 Thermochemistry To determine the heat of reaction

1½ hours

Individually

In the laboratory

A, B, C, E

8 Reaction kinetics To determine the effect of temperature on the reaction rate

1½ hours


A, B, C, E

9*

Physical Quantity

Reaction kinetics To investigate the hydrolysis of methyl ethanoate

1½ hours

Individually At home A, B, C, E

* Compulsory experiment to be carried out for assessment.


10


Report to be

completed

Skills tested

10* Ionic equilibrium The determine the dissociation constant of a weak acid using a pH meter

1½ hours

Individually/ In groups

In the laboratory

A, B, C, E

11* Equilibrium and solubility

To determine the solubility product, Ksp of lead(II) iodide

1½ hours


A, B, C, E

12* Electrochemistry - electromotive force of a cell

To investigate the effect of concentration on the electromotive force of a cell

1½ hours

Individually/ In groups

In the laboratory

A, B, C, E

13*

Physical Quantity

Electrochemistry - Faraday's Laws

To determine the value of Avogadro's constant by means of the electrolysis procedure

1½ hours


A, B, D, E

14* Qualitative analysis

To determine the cations and anions of inorganic substances

1½ hours


A, B, C, D,

E

15* Qualitative analysis

To determine the cations and anions in a mixture of inorganic salts

1½ hours


A, B, C, D,

E

16 Qualitative analysis

To determine the functional groups of organic substances

1½ hours


A, B, C, E

17* Synthesis To determine the percentage of aluminium in a sample X by means of the preparation of a complex compound of aluminium with 8-hydroxyquinoline

2 hours

In groups At home A, B, C, E

18

Technique

Synthesis To prepare and to purify a sample of benzoic acid

2 hours




11


Report to be

completed

Skills tested

19* Separation process - Chromatography

To separate and to identify the colours found in a type of commercial food dye

2½ hours

Individually/In groups

At home A, B, C, E

20*

Technique

Separation process - Extraction

To investigate the effect of solvent volume and number of extractions on the percentage of extracted product

2 hours




12

6.0 Preparation of Solutions for Volumetric Analysis

For a 0.05 mol dm-3 solution of sodium ethanedioate, Na2C2O4, with a relative formula mass of 134.0, its concentration in g dm-3 can be prepared using the following equation.

Concentration in g dm-3 = molarity × relative formula mass = 0.05 × 134 = 6.7

Standard solutions of sulphuric acid, glacial ethanoic acid, and ammonia are prepared as

follows. Step 1

By using the formula: Density = volumemass and the specifications given in the table

below, the volumes of reagents required for dilution can be calculated.

Acid Relative Molecular Mass

Density or Specific Gravity

Purity

HCl

H2SO4

HNO3

H2O2

NH3

CH3COOH

36.5 98.0 65.0 34.0 17.0 60.0

1.18 1.84 1.42 1.13

0.88-0.91 1.05

36% 98% 70% 35% 25%

99.5%

Example: To prepare 1 dm3 of 0.1 mol dm-3 solution of HCl, the volume of

concentrated acid required 3.65 100 8.591.18 36

= ´ = cm3.

Acid 0.10 mol dm-3 Volume required/ cm3

HCl

H2SO4

HNO3

H2O2

NH3

CH3COOH

3.65 9.80 6.50 3.40 1.70 6.00

8.6 5.4 6.5 8.6 7.7 5.7


13

Step 2 For more accurate work, these solutions need to be standardised using a standard solution of sodium carbonate, Na2CO3. A standard solution of sodium carbonate can be prepared in the following way: A little anhydrous sodium carbonate is dried in an evaporating dish to eliminate all traces of moisture. The substance is then cooled in a desiccator. The amount required (5.3 g dm-3 for a 0.05 mol dm-3 solution) is then weighed, dissolved, and made into a solution in a standard flask. Acid solutions are then standardised using this solution. Other concentrations of acid solutions can be prepared by diluting certain volumes of the acids and standardising them with the standard solution of sodium carbonate. 6.1 Standard solution of sodium thiosulphate Standard solutions of sodium thiosulphate, Na2S2O3.5H2O, (relative molecular

mass 248.0) cannot be prepared directly because of its salt's nature of absorbing water. For accurate work, a solution which is prepared directly will not give good results, e.g. problems which involve the determination of relative molecular mass or relative atomic mass. Prepared solutions of thiosulphate are normally standardised with potassium iodate, which will react with iodide in acid solution to liberate iodine. Potassium iodate is used because this compound is available in a pure state.

6.2 Standard solution of Fe2+ ions To prepare this solution, use FeSO4.(NH4)2SO4.6H2O (relative molecular mass

392.0), not FeSO4.7H2O. Iron(II) sulphate is easily oxidised by air. In the preparation of this solution, the double salt FeSO4.(NH4)2SO4.6H2O needs to be dissolved in dilute sulphuric acid and made up to the required volume with distilled or deionised water.

6.3 Iodine solution Iodine dissolves sparingly in water. Its solution is prepared by dissolving iodine in

a solution of potassium iodide and making up to the required volume with distilled or deionised water.

I2(s) + I−(aq) → I3

−(aq)


14

6.4 Hydrogen peroxide solution The strength of a solution of hydrogen peroxide is usually mentioned in 'volumes',

e.g: '20-volume' hydrogen peroxide, '100-volume' hydrogen peroxide, etc. For a 20-volume solution, 1 cm3 of hydrogen peroxide will decompose to yield 20 cm3 of oxygen at s.t.p.

2H2O2 → 2H2O + O2

68 g of hydrogen peroxide liberates 22.4 litres of oxygen at s.t.p.

1 g of hydrogen peroxide liberates 22.468

litres of oxygen at s.t.p.

1 litre of 20-volume hydrogen peroxide liberates 20 litres of oxygen at s.t.p.

∴1 litre of 20-volume hydrogen peroxide contains 20 68 60.8g.22.4

´ =

Therefore, to prepare a 0.1 mol dm-3 solution of H2O2, about 5.6 cm3 of

20-volume hydrogen peroxide must be diluted to make 1 litre. Other concentrations can be prepared by diluting suitable volumes of 20-volume H2O2. Hydrogen peroxide solutions cannot be kept for long periods of time because of their strong tendency to decompose. Hence, hydrogen peroxide solutions for volumetric work must be standardised with a standard solution of potassium manganate(VII) before use.

6.5 Preparation of indicator solutions 6.5.1 Methyl orange Dissolve 1 g of the solid in 1 dm3 of water. 6.5.2 Screened methyl orange Dissolve 1 g of methyl orange and 1.5 g of p-xylene cyanol in 500 cm3 of

alcohol and dilute the solution to 1 dm3 with water. 6.5.3 Phenolphthalein Dissolve 1 g of the solid in 500 cm3 of alcohol and dilute the solution to

1 dm3 with water. 6.5.4 Starch indicator (usually ≈ 1%) Make a paste of 1 g of starch with cold water, then pour boiling water and

make up to 100 cm3.


15

Experiment 1 Topic : Volumetric analysis − Acid base Purpose : To determine the exact concentration of a mineral acid, HXO4, and to

determine the relative atomic mass of the element X Materials : KA 1 is a mineral acid, HXO4.

KA 2 is a solution containing 1.70 g of OH− ions per dm3.

Phenolphthalein as indicator. Procedure : (a) Pipette 25.0 cm3 of KA 2 into a titration flask. Add two or three drops of phenolphthalein indicator and titrate this solution with KA 1. Record your readings in the table below.

Repeat the titration as many times as you think necessary to achieve accurate results. Results : (b) Record your titration readings in the table below.

Accurate Titration

Rough

Final reading/cm3

Initial reading/cm3

Volume of KA 1/cm3 (i) 25.0 cm3 of KA 2 required ……… cm3 of KA 1 for a complete reaction.

(ii) Calculate your average titre value showing the suitable titre values that you use. Questions : (c) Calculate the concentration, in mol dm-3, of solution KA 2. (d) Write a balanced ionic equation for the reaction between solution KA 1 and solution KA 2. (e) Calculate the concentration, in mol dm-3, of mineral acid HXO4 in solution KA 1. (f) If the concentration of mineral acid HXO4 in solution KA 2 is 20.1 g dm-3, calculate the relative molecular mass of HXO4. (g) Using the answer to (f), determine the relative atomic mass of element X. (h) Suggest an identity for element X.


16

Notes for Teachers Materials • KA 1 is a solution containing 8.6 cm3 of concentrated hydrochloric acid per dm3,

(0.10 mol dm-3), about 100 cm3 per candidate.

• KA 2 is a solution containing 4.00 g sodium hydroxide per dm3, (0.10 mol dm-3), about 250 cm3 per candidate.

• Phenolphthalein as an indicator Apparatus per candidate • One 25 cm3 pipette and pipette filler

• Three titration flasks

• One 50 cm3 burette

• One retort stand and clamp

• One white tile

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows:

1. Technique of transferring solution from the pipette into the titration flask

2. Technique of titration

3. Method of washing off the solution from the sides of the titration flask with distilled water before reaching the end-point

4. Method of rinsing the burette and pipette with the solution to be measured before filling up the apparatus with the solution


17

Experiment 2 Topic : Volumetric analysis − Redox

Purpose : To determine the ratio of the number of moles of hydroxyammonium ions to the number of moles of iron(III) ions participating in the reaction Materials : KA 1 is a solution containing 1.58 g of potassium manganate(VII) per

500 cm3.

KA 2 is a solution prepared by boiling 4.00 g of hydroxyammonium sulphate, (NH3OH)2SO4 per dm3

with excess iron(III) ammonium sulphate and dilute sulphuric acid.

KA 3 is 1.0 mol dm-3 sulphuric acid. Introduction : In the presence of hydrogen ions, the hydroxyammonium ion, NH3OH+ will reduce iron(III) ion to iron(II) ion while the NH3OH+ ion itself will be oxidised to dinitrogen oxide. Procedure : (a) Pipette 25.0 cm3 of KA 2 into a titration flask. Add approximately 25 cm3 of KA 3 into KA 2 and titrate this mixture with solution KA 1.


Accurate Titration

Rough

Final reading/cm3

Initial reading/cm3

Volume of KA 1/cm3 (i) 25.0 cm3 of KA 2 required ………… cm3 of KA 1 for a complete reaction.

(ii) Calculate your average titre value showing the suitable titre values that you use. Questions : (c) Calculate the concentration, in mol dm-3, of manganate(VII) ions in solution KA 1. (d) Calculate the concentration, in mol dm-3, of iron(II) ions in solution KA 2. (e) Calculate the mass of iron(II) ions in 1 dm3 of KA 2.


18

(f) Determine the number of moles of iron(III) ions required to oxidise 1 mol of hydroxyammonium ions. (g) Write a balanced redox equation between NH3OH+ ions and Fe3+ ions. (h) Why would the titration not require an external indicator?


19

Notes for Teachers Materials • KA 1 is a solution containing 3.16 g of potassium manganate(VII) per dm3, about

200 cm3 per candidate.

• KA 2 is a solution containing 37.77 g of diammonium iron(II) sulphate(VI) hexahydrate (NH4)2SO4.FeSO4.6H2O per dm3, about 200 cm3 per candidate. (Dissolve 37.77 g of solid in 200 cm3 of 1.0 mol dm-3 H2SO4 and make up the volume of solution to 1 dm3 with distilled water.)

• KA 3 is a solution containing 54.9 cm3 of concentrated sulphuric acid per dm3, about 200 cm3 per candidate.

Apparatus per candidate • One 25 cm3 pipette and pipette filler




• One 50 cm3 measuring cylinder

• One white tile

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Technique of transferring solution from the pipette into the titration flask



4. Method of rinsing the burette and pipette with the solution to be measured before filling up the apparatus with the solution


20

Experiment 3 Topic : Volumetric analysis − Acid base and redox Purpose : To determine the mass of sodium ethanedioate used to prepare a solution containing sodium ethanedioate and hydrated ethanedioic acid Materials : KA 1 is a solution containing hydrated ethanedioic acid, H2C2O4.2H2O,

and sodium ethanedioate.

KA 2 is a solution containing 3.5 g potassium manganate(VII) per dm3.

KA 3 is a solution containing 1.7 g hydroxyl ions per dm3.

KA 4 is 1.0 mol dm-3 sulphuric acid.

Phenolphthalein as indicator Procedure : (a) Pipette 25.0 cm3 KA 1 into a titration flask. Add two or three drops of phenolphthalein and titrate this solution with KA 3. Record your readings in the table below.


Accurate Titration

Rough

Final reading/cm3

Initial reading/cm3


(ii) Calculate your average titre value showing the suitable titre values that you use. (c) Pipette 25.0 cm3 of KA 1 into a titration flask. Then add 25 cm3 of KA 4. Heat this solution to about 60 °C, and titrate the solution with KA 2 until a faint pink colour persists in the solution.

Repeat the titration as many times as you think necessary to achieve accurate results.


21

Results : (d) Record your titration readings in the table below.

Accurate Titration

Rough

Final reading/cm3

Initial reading/cm3


(ii) Calculate your average titre value showing the suitable titre values that you use. Questions : (e) Calculate the concentration, in mol dm-3, of hydrated ethanedioic acid in solution KA 1. (f) Calculate the mass of ethanedioate ions, C2O4

2-, in 1 dm3 of KA 1. (g) Calculate the concentration, in mol dm-3, of ethanedioate ions which originated from the sodium ethanedioate salt. (h) Calculate the mass of sodium ethanedioate present in 1 dm3 of solution KA 1. (i) Calculate the percentage of sodium ethanedioate in solution KA 1. (j) Why was solution KA 4 added to solution KA 1 before the titration?


22

Notes for Teachers This experiment is to be conducted in pairs. Materials • KA 1 is a solution containing 3.0 g of sodium ethanedioate, Na2C2O4, and 4.0 g

hydrated ethanedioic acid, H2C2O4.2H2O, per dm3, about 250 cm3 per candidate.

• KA 2 is a solution containing 3.50 g potasium manganate(VII), KMnO4, per dm3, about 120 cm3 per candidate.

• KA 3 is a solution containing 4.00 g sodium hydroxide per dm3, about 120 cm3 per candidate.

• KA 4 is 1.0 mol dm-3 sulphuric acid, about 120 cm3 per candidate.

• Phenolphthalein as indicator Apparatus per group (2 candidates) • Two 25 cm3 pipettes and pipette fillers

• Two 50 cm3 burettes

• Six titration flasks

• Two retort stands and clamps


• Two white tiles

• One wash bottle filled with distilled water

• One thermometer 0 °C–100 °C (by 1.0 °C) Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Technique of using burette, pipette, and measuring cylinder to measure volume of

solution

2. Technique of heating




23

Experiment 4 Topic : Volumetric analysis − Purity and stoichiometry Purpose : To determine the purity of a sample of sodium sulphite crystals Materials : KA 1 is 0.05 mol dm-3 aqueous iodine.

KA 2 is 0.1 mol dm-3 aqueous sodium thiosulphate.

KA 3 is a solution containing 24.0 g of anhydrous sodium sulphite, Na2 SO3, per dm3.

KA 4 is 2 g solid sodium hydrogen carbonate. Starch as indicator Introduction : The sulphite ion can be oxidised quantitatively to the sulphate ion by iodine in the presence of the hydrogen carbonate ion.

SO3 2 − + I2 + H2O SO4

2 − + 2HI

2HI + 2HCO3−

2I − + 2H2O + 2CO2

If a solution of sodium sulphite is added to an excess of a standard solution of iodine, the excess iodine in the resulting solution can be titrated with a standard solution of sodium thiosulphate. Hence the concentration of sodium sulphite can be determined. Procedure : (a) Pipette 50.0 cm3 of KA 1 into a titration flask. Using another pipette, place 25.0 cm3 of KA 3 slowly into this titration flask containing KA 1 and shake. Add 2 g of KA 4 and shake the flask again. Titrate the resulting solution with KA 2 using starch as indicator.


Accurate Titration

Rough

Final reading/cm3

Initial reading/cm3


(ii) Calculate your average titre value showing the suitable titre values that you use.


24

Questions : (c) Write a balanced equation for the reaction between iodine and the thiosulphate ion. (d) Calculate the volume of I2 that did not react with the sulphite ions. (e) Using your answer to (d), calculate the volume of I2 that reacted with the sulphite ions. (f) Using your answer to (e),

(i) calculate the concentration, in mol dm-3, of the sulphite ions in solution KA 3,

(ii) calculate the mass of Na2SO3 present in 250 cm3 of KA 3. (g) Using your answer to (f)(ii), calculate the percentage purity of Na2SO3 that you used.


25

Notes for Teachers Materials • KA 1 is a 0.025 mol dm-3 aqueous iodine prepared by dissolving 6.35 g of solid iodine

in 10% solution of potassium iodide per dm3, about 250 cm3 per candidate.

• KA 2 is a solution containing 12.41 g of sodium thiosulphate per dm3, about 200 cm3 per candidate.

• KA 3 is a solution containing 3.15 g of anhydrous sodium sulphite, Na2SO3, per dm3, about 150 cm3 per candidate.

• KA 4 is a 2 g packet of solid sodium hydrogen carbonate, about 5 packets per candidate.

• Starch as indicator Apparatus per candidate • One 25 cm3 pipette and pipette filler

• One 50 cm3 pipette




• One white tile

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Method of handling the pipette

2. Method of holding and shaking the titration flask during the titration process

3. Addition of indicator at the appropriate time


26

Experiment 5 Topic : Volumetric analysis − stoichiometry Purpose : To determine the exact concentration of a monobasic acid, HX Question : You are provided with a monobasic acid, HX, with a concentration in

the range of 0.5 mol dm-3 to 1.0 mol dm-3. You are required to plan and carry out an experiment to determine the exact concentration of the HX solution provided.


27

Notes for Teachers This experiment is to be conducted after the teacher has taught the topic on Ionic Equilibrium. Materials • A suitable monobasic acid is hydrochloric or ethanoic acid, about 150 cm3 per

candidate.

• A suitable base is aqueous ammonia, solid sodium hydroxide, or solid sodium carbonate with suitable volume or weight as required by the student.

• A suitable indicator is phenolphthalein or methyl orange.

• Distilled water, about 250 cm3 per candidate. Apparatus per candidate • 250 cm3 volumetric flask and stopper

• Electric balance ±0.01 g or equivalent (common use)

• One 25.0 cm3 pipette and pipette filler

• One 100 cm3 volumetric flask and stopper

• Two 50 cm3 burettes


• One white tile


• Spatula


• Other suitable fittings and apparatus Skills A, B, D, and E Examples of skills A that can be observed are as follows: 1. Reasonable quantities of substance used

2. Correct way of adding the indicator


28

Experiment 6 Topic : Thermochemistry Purpose : To determine the heat of neutralisation of a strong acid with a strong base Materials : KA 1 is 1.0 mol dm-3 hydrochloric acid.

KA 2 is a 1.0 mol dm-3 solution of a strong acid W.

KA 3 is 1.0 mol dm-3 aqueous sodium hydroxide.

KA 4 is 1.0 mol dm-3 nitric acid.

KA 5 is 1.0 mol dm-3 aqueous potassium hydroxide. Procedure : (a) By means of a pipette, place 10.0 cm3 of KA 1 into a plastic cup. Record the temperature of KA 1 as the initial temperature of mixture X in the table below.

By means of a measuring cylinder, add 30 cm3 of solution KA 3 into the plastic cup containing KA 1. Stir mixture X carefully with a thermometer and record the highest temperature attained in the table below. Pour away mixture X from the plastic cup. Then clean and rinse the cup with distilled water.

Repeat the above procedure using

(i) 10.0 cm3 of KA 2 to replace KA 1 to obtain mixture Y, and

(ii) 10.0 cm3 of KA 4 and 30 cm3 of KA 5 to replace KA 1 and KA 3 respectively to obtain mixture Z. Results : (b) Complete the table below.

Mixture X KA 1 + KA 3

Mixture Y KA 2 + KA 3

Mixture Z KA 4 + KA 5

Highest temperature/°C

Initial temperature/°C

Increase in temperature/°C


29

Questions : (c) If 4.2 Joules is required to raise the temperature by 1 °C for 1 cm3 of solution, calculate the heat released for each of the experiments conducted. (d) Calculate the number of moles of the following solutions added into the plastic cup.

(i) Sodium hydroxide

(ii) Potassium hydroxide

(iii) Hydrochloric acid

(iv) Nitric acid

(v) Acid W (e) Write an ionic equation for the reaction taking place in mixtures X, Y, and Z. (f) Calculate the heat of neutralisation for each reaction. (g) (i) Explain why the values of the heat of neutralisation you obtained differ in mixtures X, Y, and Z.

(ii) The heat of neutralisation between a strong acid and a strong base is −57.3 kJ mol−1. How would you improve the given procedure so that an approximate value of −57.3 kJ mol−1 could be obtained?


30

Notes for Teachers Materials • KA 1 is a solution containing 86.0 cm3 of concentrated hydrochloric acid per dm3,

about 20 cm3 per candidate.


• KA 3 is a solution containing 40.0 g of sodium hydroxide per dm3, about 80 cm3 per candidate.

• KA 4 is a solution containing 65.0 cm3 of concentrated nitric acid per dm3, about 20 cm3 per candidate.

• KA 5 is a solution containing 56.0 g of potassium hydroxide per dm3, about 50 cm3 per candidate.

Apparatus per candidate • One 10 cm3 pipette and pipette filler

• One thermometer 0 °C−110 °C (±0.2 °C)


• One plastic/polystyrene cup

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills B that can be observed are as follows: 1. Correct method of using the thermometer, like stirring the solution to ensure thorough

mixing and to measure the highest temperature reached

2. The eye level must be correct and exact while taking temperature readings so as to avoid errors due to parallax

3. Take temperature readings of a suitable accuracy

4. The initial and highest temperatures are to be recorded to one place of decimal

5. Correct measurement of an increase in temperature from the readings of the initial and highest temperatures attained


31

Experiment 7 Topic : Thermochemistry Purpose : To determine the heat of reaction Materials : KA 1 is 2.0 mol dm-3 hydrochloric acid.

KA 2 is solid anhydrous sodium carbonate.

KA 3 is solid sodium hydrogen carbonate. Procedure : (a) Using a burette, run 30.00 cm3 of KA 1 into a plastic cup. Leave the cup with its contents to stand for a few minutes, then record the temperature of the solution in the table below.

Weigh a stoppered test-tube containing KA 2 and record its weight in the table below. At one go, transfer all of the KA 2 into the plastic cup containing KA 1. Ensure that all solid leaving the test-tube enters the plastic cup and no liquid is lost through splashing. Stir the solution carefully with the thermometer, and record the highest temperature attained. Reweigh the empty test-tube and record its weight in the table below.

Repeat the above procedure using KA 3 to replace KA 2. Results : (b) Record all your readings and weighings in the table below.

KA 2 KA 3

Weight of test-tube + solid/g

Weight of empty test-tube/g

Weight of solid/g

Initial temperature of acid/°C

Final temperature of mixture/°C

Temperature change/°C

Questions : (c) Assuming that the heat loss to the plastic cup, thermometer, and surroundings can be ignored and the specific heat capacity and density of all the solutions are 4.2 J g−1 K−1 and 1.0 g cm−3 respectively, calculate

(i) the heat change in the reactions involving KA 1 and KA 3,

(ii) the number of moles of anhydrous sodium carbonate and sodium hydrogen carbonate in KA 2 and KA 3 respectively,

(iii) the enthalpy change for the reactions of KA 2 and KA 3 with hydrochloric acid respectively.


32

(d) Write balanced equations for the reactions of KA 2 and KA 3 with hydrochloric acid. (e) Draw an energy level diagram for the related reactions. (f) Calculate ΔH for the conversion reaction of sodium hydrogen carbonate to sodium carbonate using Hess Law and (e).


33

Notes For Teachers Materials • KA 1 is a solution containing 172 cm3 of concentrated hydrochloric acid per dm3, about

100 cm3 per candidate.

• KA 2 is 2.00 g to 2.40 g of solid anhydrous sodium carbonate in a stoppered test-tube; one test-tube of KA 2 per candidate.

• KA 3 is 2.70 g to 3.10 g of sodium hydrogen carbonate in a stoppered test-tube; one test-tube of KA 3 per candidate.

Apparatus per candidate • One 50 cm3 burette


• One plastic/polystyrene cup

• One thermometer 0 °C–110 °C (±0.2 °C)


• Electric balance ±0.01 g (common use) Skills A, B, C, and E Examples of skills B that can be observed are as follows: 1. Measurement of the initial temperature is only carried out when the temperature is

stable.

2. Correct method of weighing to obtain an exact weight of KA 2

3. Weights to be recorded to the nearest 0.01 g in the correct spaces

4. Temperatures to be recorded to the nearest 0.2 °C in the correct spaces


34

Experiment 8 Topic : Reaction kinetics Purpose : To determine the effect of temperature on the reaction rate Materials : KA 1 is 0.15 mol dm-3 aqueous potassium iodide.

KA 2 is 0.5% starch solution.

KA 3 is 0.05 mol dm-3 aqueous sodium thiosulphate.

KA 4 is 0.1 mol dm-3 aqueous hydrogen peroxide.

KA 5 is 0.1 mol dm-3 sulphuric acid. Procedure : (a) Pipette 25.0 cm3 of KA 1 into a conical flask. By means of a measuring cylinder, add 10 cm3 of KA 2 and 25 cm3 of distilled water to the solution. Then run in 10.00 cm3 of KA 3 from the burette. Record the temperature of the mixture in the table below.

Using a measuring cylinder, place 50 cm3 of KA 4 and 20 cm3 of KA 5 into a beaker. Pour the whole solution quickly from this beaker to the contents in the conical flask and at once start the stopwatch. Shake the conical flask from time to time and record the time when the solution turns blue. Note the time taken to the nearest second. If no colour appears after two minutes, repeat this part once.

Repeat the above procedure at different temperatures, i.e 10 °C below the room temperature as well as 10 °C and 20 °C above the room temperature. Results : (b) Record and complete your readings in the table below.

Mixture 1 2 3 4

Volume of KA 1/cm3 25 25 25 25


Volume of distilled water/cm3 25 25 25 25




Temperature, T/°C

Time, t/s

1/s1 −

t


35

Questions : (c) Plot a graph of

t1 against T.

(d) From your graph, what could be the effect of temperature on the reaction rate? (e) What information can you obtain from the gradient of the graph in (c)? (f) Using your graph,

(i) compare the rate of reaction at 30 °C with the rate of reaction at 40 °C,

(ii) give an explanation for your answer.


36

Notes for Teachers Materials • KA 1 is a solution containing 24.9 g of potassium iodide per dm3, about 150 cm3 per

candidate.

• KA 2 is a 0.5% starch solution, about 50 cm3 per candidate.

• KA 3 is a solution containing 12.41 g of sodium thiosulphate per dm3, about 50 cm3 per candidate.

• KA 4 is a solution containing 8.6 cm3 of hydrogen peroxide (35%) per dm3, about 300 cm3 per candidate.


• Ice and hot water are used as water bath and also to obtain different temperatures.

• Distilled water, about 150 cm3 per candidate. Apparatus per candidate • One 25 cm3 pipette and pipette filler





• One conical flask

• One stopwatch

• One 150 cm3 beaker

• One thermometer 0 °C–100 °C (±1.0 °C)


• One white tile Skills A, B, C, and E Examples of skills B and C that can be observed are as follows: 1. Determination of the correct time taken to measure the effect of temperature on the rate

of reaction

2. Be accurate in noting the time when the blue colour appears

3. Accurate time and temperature readings are recorded in the correct spaces

4. Be able to plot the correct graph from the information obtained

5. Correct interpretation of the graph plotted


37

Experiment 9 Topic : Reaction kinetics Purpose : To investigate the hydrolysis of methyl ethanoate Materials : KA 1 is 0.5 mol dm-3 hydrochloric acid.

KA 2 is aqueous sodium hydroxide of concentration 4.0 g dm-3.

KA 3 is methyl ethanoate.

Distilled water Procedure : (a) Using a measuring cylinder, place 100 cm3 of KA 1 into a 250 cm3 conical flask. Using a smaller measuring cylinder, add 5 cm3 of KA 3 into the 250 cm3 conical flask. When about half of the KA 3 have been added, start the stopwatch and shake the flask carefully for a while.

Then pipette immediately 5.0 cm3 of solution from this 250 cm3 conical flask and transfer the sample to a 250 cm3 titration flask containing 100 cm3 of ice water. Note the time when half of the sample in the pipette has been transferred. When all of the 5.0 cm3 is transferred, add one or two drops of phenolphthalein and titrate this solution immediately with solution KA 2. Record your results in the table below.

(b) Repeat the procedure in the second paragraph above for sample 2, 3, and 4 withdrawn from the 250 cm3 conical flask in the specific time intervals of 10, 20, and 30 minutes respectively. Record all your results in the table below.

(c) Repeat procedure (a) in the first paragraph but substitute solution KA 1 with distilled water to prepare sample 5. Repeat the procedure in the second paragraph for sample 5 after 30 minutes have elapsed. You are advised to continue writing your report while waiting for the 30 minutes to end. Results : (d) Record and complete your readings in the table below.

Sample 1 2 3 4 5

Time of transferring sample/minute 10.0 20.0 30.0 40.0

Final reading/cm3

Initial reading/cm3

Volume of KA 3/cm3


38

Questions : (e) Write a balanced equation for the hydrolysis of methyl ethanoate. (f) What is the purpose of titrating the sample of reaction mixture with KA 2? (g) Plot a graph showing how the volume of KA 2 used in the titration varies with time. (h) Why was the sample of reaction mixture added to 100 cm3 of ice water before titration?

(i) Using the same axes as in (g), sketch an expected graph for the hydrolysis of the ester conducted at the same temperature but with 0.1 mol dm-3 ethanoic acid. Explain your answer. (j) Based on the results of the experiments for samples 4 and 5, state the role of hydrochloric acid in the experiments.


39

Notes for Teachers Materials • KA 1 is hydrochloric acid, 0.5 mol dm-3, about 250 cm3 per candidate.

• KA 2 is a solution of sodium hydroxide, 4.0 g dm-3, about 250 cm3 per candidate.

• KA 3 is methyl ethanoate, about 10 cm3 per candidate.

• Phenolphthalein as indicator

• Ice water, about 600 cm3 per candidate

• Distilled water, about 150 cm3 per candidate Apparatus per candidate • One 50 cm3 burette


• Three 250 cm3 titration flasks

• One 10 cm3 graduated pipette and pipette filler



• One 250 cm3 conical flask

• One stopwatch

• One white tile

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Technique of using the burette, pipette, and measuring cylinder to measure the volume

of a solution

2. Technique of using the stopwatch

3. Ability to follow the procedure systematically


40

Experiment 10 Topic : Ionic equilibrium Purpose : To determine the dissociation constant of a weak acid using a pH meter Materials : KA 1 is a 1.0 mol dm-3 solution of a weak acid. Procedure : (a) Prepare four 100 cm3 beakers labelled W, X, Y, and Z. Pipette 20.0 cm3 of KA 1 into beaker W. Then pipette 2.0 cm3 of KA 1 from beaker W into beaker X. Run 18.00 cm3 of distilled water from the burette into beaker X. Stir the solution. Pipette 2.0 cm3 of the solution from beaker X into beaker Y. Add 18.0 cm3 of distilled water into beaker Y. Repeat the same procedure for beaker Z using 2.0 cm3 of solution from beaker Y, and then dilute. Stir the solution produced.

Using the pH meter, determine the pH value of each of the solutions produced in beakers W, X, Y, and Z. Record the pH readings and complete the table below.

(Note: The final volume in beakers W, X, and Y is 18.0 cm3 whereas it is 20.0 cm3 in beaker Z.) Results : (b) Record and complete your readings in the table below.

Weak acid Molarity/ mol dm-3 pH [H+] Degree of

dissociation Dissociation

constant

W

X

Y

Z

Questions : (c) Plot a graph of pH against the molarity of the solution. (d) What is the effect of dilution on the pH of the solution? (e) What is the effect of dilution on the degree of dissociation? (f) Calculate the value of the dissociation constant for each of acid solutions KA 1 of different concentrations. (g) What is the effect of dilution on the dissociation constant of the acid?


41

Notes for Teachers The teacher is advised to calibrate the pH meter with the standard buffer solution before carrying out the experiment. Materials • KA 1 is a solution containing 5.7 cm3 of ethanoic acid (99.5%) per dm3, about 30 cm3

per candidate.

• Distilled water, about 50 cm3 per candidate Apparatus per candidate/group • pH meter

• Four 100 cm3 beakers

• Four pieces of paper label

• One 10 cm3 pipette and pipette filler

• One 1 cm3 graduated pipette



• One glass rod

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Ensure that the "bulb" electrode of the pH meter is fully immersed in the solution

2. The measurement of pH values must start off with the most dilute solution


42

Experiment 11 Topic : Equilibrium and solubility Purpose : To determine the solubility product, Ksp, of lead(II) iodide Materials : KA 1 is 0.25 mol dm-3 aqueous lead(II) nitrate.

KA 2 is 0.10 mol dm-3 aqueous lead(II) nitrate.



KA 5 is 0.01 mol dm-3 aqueous potassium iodide. Introduction : Research on chemical systems that are slightly soluble in water needs to take into consideration the equilibrium phenomenon involved. The equilibrium constant or solubility product, Ksp, for such systems can be obtained by taking into account the concentration of the ions of solutes in saturated solutions. Procedure : (a) Titrate 25.0 cm3 of KA 1 with KA 5. The end point is achieved when a precipitate appears.

Repeat the experiment with KA 2, KA 3, and KA 4. Results : (b) Record and complete your readings in the table below.

Solution KA 1 KA 2 KA 3 KA 4

[Pb(NO3)2]o/mol dm-3 0.25 0.10 0.05 0.02

[KI]o/mol dm-3 0.01 0.01 0.01 0.01

Volume of Pb(NO3)2, Vo/cm3

Volume of KI, V/cm3

(Vo + V)/cm3


43

Questions : (c) From your titre values, calculate the concentration of lead(II) ions and iodide ions at end point for each of solutions KA 1, KA 2, KA 3, and KA 4. Enter the concentration values obtained in the table below and complete the table.

Solution KA 1 KA 2 KA 3 KA 4

[Pb2+]

[I-]

[Pb2+][I-]2

(d) Sketch a graph of [Pb2+][I-]2 against [Pb2+]. (e) Comment on the values of the ionic product of PbI2. (f) Calculate an average value for the solubility product of lead(II) iodide. (g) What is the effect of increasing the concentration of lead(II) ions on Ksp of PbI2?


44

Notes for Teachers Materials • KA 1 is a solution containing 82.75 g of lead(II) nitrate per dm3, about 50 cm3 per

candidate.

• KA 2 is a solution containing 33.10 g of lead(II) nitrate per dm3, about 50 cm3 per candidate.



• KA 5 is a solution containing 1.66 g of potassium iodide per dm3, about 100 cm3 per candidate.

Apparatus per candidate • One 50 cm3 burette


• Four 250 cm3 conical flasks


• One white tile

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills B that can be observed are as follows: 1. Ensuring that the last titration is done with the appearance of the first yellow precipitate

2. Recording exact burette readings in the correct spaces

3. Plotting a correct graph based on the data obtained


45

Experiment 12 Topic : Electrochemistry − Electromotive force of a cell Purpose : To investigate the effect of concentration on the electromotive force of a

cell Materials : KA 1 is 1.0 mol dm-3 aqueous copper(II) sulphate.

KA 2 is 2.0 mol dm-3 aqueous zinc sulphate.





A saturated solution of potassium chloride Procedure : (a) By means of measuring cylinders, fill beaker A with 50.0 cm3 of KA 1 and beaker B with 50 cm3 of KA 2. Immerse a strip of filter paper into the saturated solution of potassium chloride; then dip the ends of the filter paper into the two beakers A and B to build a salt bridge. Clean the copper and zinc plates with sandpaper, wash with distilled water, and dry. Clip the copper plate with the crocodile clip and connect it to the end of the potentiometer to which the positive terminal of the accumulator is connected. The zinc metal is connected to a galvanometer to which a jockey is attached. The negative terminal of the accumulator is then connected to the other end of the potentiometer as shown in the diagram below.

Dip the two metal plates into their respective solutions. After one minute has elapsed, touch the jockey along the length of the potentiometer wire until the galvanometer shows a zero reading indicating no current flow. Do not slide the jockey along the length of the potentiometer wire to avoid a build up of resistance. Note down the length of the potentiometer wire as x cm and record your readings in the table on the next page.


46

Repeat the experiment above by replacing solution KA 2 with solutions as shown in the table below. New filter papers are to be used for every new solution.

Calculate Eθcell using the following formula.

Eθcell V2

wireterpotentiomeofLength×=

x

Results : (b) Length of potentiometer wire = ………… cm

Experiment Beaker A Beaker B Length of wire x/cm Eθ

cell/V [Zn2+ ]/ mol dm-3 lg [Zn2+]

1 50 cm3 KA 1 50 cm3 KA 2

2 50 cm3 KA 1 50 cm3 KA 3

3 50 cm3 KA 1 50 cm3 KA 4

4 50 cm3 KA 1 50 cm3 KA 5

5 50 cm3 KA 1 50 cm3 KA 6

Questions : (c) Write a cell diagram for the electrochemical system. (d) Write half-cell equations for the reactions taking place in beakers A and B and hence write an equation for the overall cell reaction. (e) Plot a graph of Eθ

cell against lg [Zn2+] in beaker B and explain how the e.m.f. of the cell varies with the concentration of Zn2+ in beaker B. (f) What will happen to the Eθ

cell value if

(i) the solution in beaker A is replaced with 0.1 mol dm-3 aqueous copper(II) sulphate,

(ii) the solution in beaker B is replaced with 0.1 mol dm-3 aqueous aluminium chloride, and the plate of zinc metal is replaced with aluminium metal?


47

Notes for Teachers The teacher has to ensure that all solutions (bulk solution) prepared are homogenous and are prepared ONE day in advance before carrying out the experiment. Materials • KA 1 is a solution containing 249.5 g of CuSO4.5H2O per dm3, about 100 cm3 per

candidate.

• KA 2 is a solution containing 574.8 g of ZnSO4.7H2O per dm3, about 100 cm3 per candidate.





• A saturated solution of potassium chloride, about 50 cm3 per candidate Solution KA 3 can also be prepared by diluting solution KA 2 once.

Solutions KA 4, KA 5, and KA 6 can also be prepared by diluting solution KA 3 as follows:

Solution KA 4 is prepared by diluting KA 3 ten times.




48

Apparatus per candidate • Five strips of filter paper about 15 cm × 1 cm

• One zinc plate 7 cm × 2 cm

• One copper plate 7 cm × 2 cm

• One galvanometer (zero centre)

• One potentiometer or Wheatstone bridge

• One jockey

• Five 30 cm connecting wires with crocodile clips

• One 2 volts accumulator or two dry cells (each 1.5 V)

• Two 50 cm3 measuring cylinders

• Two 100 cm3/150 cm3 beakers

• One piece of sandpaper

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills B that can be observed are as follows: 1. Skill in measuring the length of the potentiometer wire and taking the zero reading on

the galvanometer

2. Skill in setting up the circuit with the potentiometer wire and salt bridge

3. Skill in transferring solutions into the container used each time an experiment is repeated


49

Experiment 13 Topic : Electrochemistry − Faraday's Laws Purpose : To determine the value of Avogadro's constant by means of the

electrolysis procedure Question : You are required to plan and to carry out an experiment to determine a

value for the Avogadro's constant by the electrolysis procedure.


50

Notes for Teachers Materials • Solution containing 250 g of CuSO4.5H2O per dm3, about 300 cm3 per candidate

• Propanone, about 100 cm3 per candidate

• Distilled water, about 200 cm3 per candidate Apparatus per candidate • One 100 cm3 measuring cylinder


• Two pieces of copper plates measuring 5 cm × 4 cm × 0.2 cm

• Five connecting wires with crocodile clips

• One ammeter, 0 A-3 A

• One rheostat, 11 Ω

• One switch

• Four dry cells or source of direct current 6 V

• One stopwatch

• Hair dryer (common use)

• Electric balance ± 0.01 g (common use)


• Other suitable fittings and apparatus Skills A, B, D, and E Examples of skills D that can be observed are as follows: 1. Neat and proper planning following common procedures

2. Selection, setting up of apparatus, and use of materials correctly and completely

3. To obtain and to record the mass of both the copper plates at the anode and the cathode before and after the electrolysis process

4. Time planning to be compatible with the experiment


51

Experiment 14 Topic : Qualitative analysis Purpose : To determine the cations and anions of inorganic substances Procedure : (a) Solids KA 1 and KA 2 are simple salts. Carry out the following experiments with solid KA 1 to identify its cation and anion.

(b) You are then required to plan and to carry out a few experiments to identify the cation and anion present in solid KA 2.

In all the experiments, the reagent should be added gradually until no further change is observed. Record your observations and the deductions you make from them in the spaces provided. Deduce what you can about KA 1 and KA 2. Observations should include details of colour changes, precipitates, and tests on gases evolved, and you should indicate clearly at which stage in a test a change occurs. Tests on KA 1

Test Observation Deduction

(c) Add dilute hydrochloric acid to a small amount of solid KA 1, then warm gently.

(d) Dissolve solid KA 1 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (vi).

(i) Add aqueous sodium hydroxide, then in excess.

(ii) Add aqueous ammonia, then in excess followed by aqueous ammonium chloride.

(iii) Add aqueous iron(III) chloride, then warm.

(iv) Add aqueous silver nitrate, followed by dilute nitric acid.

(v) Add aqueous disodium hydrogen phosphate.

(vi) Add aqueous potassium chromate(VI) followed by dilute hydrochloric acid.

Identity of KA 1: …………………………………………..…………………………………...


52

Tests on KA 2


Identity of KA 2: …..…………………………………………………………………………...


53

Notes for Teachers 1. The teacher has to supply different salts to each of the classes taught.

2. The teacher has to supply a different salt each year to the students. Materials • KA 1 is solid MgS2O3 or MgSO3 or CuSO3 or Ca(CH3COO)2 or Pb(CH3COO)2 or

Zn(CH3COO)2.

• KA 2 is solid CuCO3 or MgCO3 or CaCO3 or MnCO3 or NiCO3 or BaCl2 or MgCl2 or CaCl2.

• Common acids (concentrated and dilute)

• Common alkalis (concentrated and dilute)

• Aqueous solution of iron(III) chloride, approximately 50 g dm-3 Dissolve 135 g of solid iron(III) chloride in distilled water containing 20 cm3 of

concentrated hydrochloric acid and make up the volume of solution to 1 dm3.

• Aqueous solution of ammonium chloride, approximately 50 g dm-3

• Aqueous solution of silver nitrate, approximately 50 g dm-3

• Aqueous solution of disodium hydrogen phosphate, approximately 50 g dm-3

• Aqueous solution of potassium chromate(VI), approximately 50 g dm-3

• Reagents to test KA 2 Apparatus per candidate • One test-tube rack with six test tubes

• One hard glass test-tube with delivery tube

• One test-tube holder

• One spatula

• One filter funnel and two pieces of filter paper

• One teat pipette

• One bunsen burner

• Red and blue litmus papers

• Wooden splint

• One wash bottle filled with distilled water Skills A, B, C, D, and E Examples of skills B and C that can be observed are as follows: 1. Correct observations for each of the tests done.

2. Correct deductions which are consistent with correct observations.


54

Experiment 15 Topic : Qualitative analysis Purpose : To determine the cations and anions in a mixture of inorganic salts Procedure : (a) KA 1 and KA 2 are mixtures of two salts. Carry out the following experiments with solid KA 1 to identify its cations.

(b) You are then required to plan and to carry out a few experiments to identify the anions present in solid KA 2.

In all the experiments, the reagent should be added gradually until no further change is observed. Record your observations and the deductions you make from them in the spaces provided. Deduce what you can about the cations in KA 1 and anions in KA 2. Observations should include details of colour changes, precipitates, and tests on gases evolved, and you should indicate clearly at which stage in a test a change occurs. Tests on KA 1


(c) Dissolve all of solid KA 1 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (v).

(i) Add aqueous sodium hydroxide, then in excess, and warm.

(ii) Add aqueous potassium iodide.

(iii) Add aqueous potassium chromate(VI).

(iv) Add aqueous sodium ethanoate, then warm.

(v) Add aqueous sodium carbonate, then warm.

Identity of cations present in KA 1: ..……………………………………………...…………...


55

Tests on KA 2


Identity of anions present in KA 2: …………………………………..………………………...


56

Notes for Teachers Materials • KA 1 is a mixture of solids Al2(SO4)3 and (NH4)2SO4

• KA 2 is a mixture of solids KI and KNO3

• Common acids (concentrated and dilute)

• Common alkalis (concentrated and dilute)

• Devarda's alloy

• Aqueous solution of potassium iodide, about 50 g dm-3

• Aqueous solution of potassium chromate(VI), about 50 g dm-3

• Aqueous solution of sodium ethanoate, about 50 g dm-3

• Aqueous solution of sodium chlorate(I), about 50 g dm-3

• Aqueous solution of sodium carbonate, about 50 g dm-3

• Aqueous lead(II) nitrate, about 50 g dm-3

• Other reagents to test for iodide and nitrate ions Apparatus per candidate • One test-tube rack and six test-tubes

• One hard glass test-tube and delivery tube

• One test-tube holder

• One spatula

• One filter funnel and two pieces of filter paper



• Red and blue litmus papers

• Wooden splint

• One wash bottle filled with distilled water Skills A, B, C, D, and E Examples of skills B and C that can be observed are as follows: Tests on KA 1. Correct observations for each of the tests done.

2. Correct deductions which are consistent with correct observations.


57

Experiment 16 Topic : Qualitative analysis Purpose : To determine the functional groups of organic substances Procedure : (a) KA 1 and KA 2 are organic compounds. Compound KA 1 contains one functional group whereas compound KA 2 contains two functional groups. Carry out the following experiments to identify the functional groups present in KA 1 and KA 2.

(b) You are then required to plan and to carry out one more experiment to confirm the functional groups present in KA 2.

In all the tests, the reagent should be added gradually until no further change is observed. Record your observations and deductions you make from them in the spaces provided. Deduce what you can about KA 1 and KA 2. Observations should include details of colour changes, precipitates, and tests on gases evolved, and you should indicate clearly at which stage in a test a change occurs. Tests on KA 1


(c) Add 2 to 3 drops of KA 1 to distilled water and shake, then add dilute hydrochloric acid followed by aqueous sodium hydroxide.

(d) Add one drop of KA 1 to distilled water and shake, then add one drop of sodium chlorate(I) solution.

(e) Add 2 to 3 drops of KA 1 to 2 cm3 of hydrochloric acid and shake, then add bromine water until the solution turns yellow. Shake and allow to stand.

(f) Dissolve 2 to 3 drops of KA 1 in 2 cm3 of hydrochloric acid and cool to 5 °C. Add cold sodium nitrite solution. Then add cold alkaline phenol solution to the mixture.

Identity of functional group in KA 1: …………………………………………………..……...


58

Tests on KA 2


(g) Add distilled water to a small amount of KA 2 and shake, then add aqueous sodium hydroxide, followed by dilute hydrochloric acid.

(h) Fill a test-tube with approximately 1 cm height of KA 2, then add aqueous sodium carbonate.

(i) Add 1 cm3 to 2 cm3 of methanol to a small amount of KA 2 and shake, and then add 1 or 2 drops of concentrated sulphuric acid. Warm the mixture. Let it cool. Then pour into a beaker containing distilled water.

Identity of functional groups in KA 2: ……………………………………….………………...


59

Notes for Teachers Materials • KA 1 is 5 cm3 of liquid aniline (phenylamine). • KA 2 is solid salicylic acid. • Common acids (concentrated and dilute) • Common alkalis (concentrated and dilute) • Bromine water Dissolve bromine solution in water to make a saturated solution. • Alkaline phenol solution Dissolve a little of the solid phenol in enough aqueous solution of sodium hydroxide.

Cool the solution to a temperature of less than 8°C. • Aqueous solution of iron(III) chloride Dissolve 135 g of solid iron(III) chloride in distilled water containing 20 cm3 of

concentrated hydrochloric acid and make up the volume of the solution to 1 dm3. • Sodium nitrite solution Dissolve sodium nitrite in water until a saturated solution is obtained and then cool the

solution to a temperature of less than 8°C. • Aqueous solution of sodium carbonate, approximately 50 g dm-3 • Sodium chlorate(I) solution • Ice cubes • Methanol Apparatus per candidate • One test-tube rack and six test-tubes • One hard glass test-tube and delivery tube • One test-tube holder • One spatula • One filter funnel and two pieces of filter paper • One teat pipette • One bunsen burner • Blue and red litmus papers • Wooden splint • One wash bottle filled with distilled water • One thermometer −10 °C to 110 °C • Refrigerator (common use) Skills A, B, C, and E Examples of skills A that can be observed are as follows:

• Reagents to be added slowly so that all the stages of observation can be recorded


60

Experiment 17 Topic : Technique − Synthesis Purpose : To determine the percentage of aluminium in a sample X by means

of the preparation of a complex compound of aluminium with 8-hydroxyquinoline.

Materials : KA 1 is a solution of 8-hydroxyquinoline in ethanoic acid.

KA 2 is 2 mol dm-3 aqueous ammonium ethanoate.

KA 3 is sample X.

KA 4 is 2 mol dm-3 hydrochloric acid. Introduction : Aluminium in a certain sample can be determined quantitatively by means of the process of formation of complex compounds, for example, an alum complex is produced by the reaction of an alum with 8-hydroxyquinoline.

Procedure : (a) Weigh out accurately between 0.25 g and 0.30 g of KA 3. Record your readings in the table below.

Mass of container + KA 3/g

Mass of empty container/g

Mass of KA 3/g

Place all of KA 3 into a 250 cm3 beaker, and add 150 cm3 of distilled water followed by one drop of KA 4. Warm the mixture to a temperature between 60 °C and 70 °C. Then add 25 cm3 of solution KA 1, followed slowly by 50 cm3 of solution KA 2. A precipitate will be formed. Remove the beaker. Stir this solution for half an hour using a magnetic stirrer.

Weigh an empty crucible and record your readings in the table on the next page. Filter the solution above and wash the precipitate with cold distilled water. Transfer the precipitate into an empty crucible and dry the precipitate in the oven at about 120 °C. Cool and weigh the crucible together with its contents.


61

Results : (b) Record your readings in the table below.

Mass of crucible + precipitate/g

Mass of empty crucible/g

Mass of precipitate/g

Questions : (c) Explain

(i) why the mixture of solutions KA 1 and KA 2 needs to be stirred for half an hour using the magnetic stirrer,

(ii) why the complex precipitate is washed with cold water. (d) How would you ensure whether the complex precipitate obtained is completely dried? (e) Calculate the mass of 1 mole of complex compound with the formula Al(C9H6NO)3 . (f) Calculate the percentage of aluminium in the complex compound. (g) Calculate the percentage of aluminium in sample X.


62

Notes for Teachers 1. The experiment is conducted in groups.

2. The students are required to submit the product of the experiment together with their reports.

Materials • KA 1 is a solution of 8-hydroxyquinoline prepared by dissolving 2 g of

8-hydroxyquinoline in 100 cm3 of 2 mol dm-3 ethanoic acid, about 50 cm3 per group.

• KA 2 is a solution containing 154 g of CH3COONH4 per dm3, about 100 cm3 per group.

• KA 3 is a potassium alum, KAl(SO4)2 .12H2O, about 0.25 g to 0.30 g per group.

• KA 4 is a solution containing 172.0 cm3 of concentrated hydrochloric acid per dm3, about 10 cm3 per group.

• Distilled water, about 200 cm3 per group

• Ice cubes Apparatus per group • Electric balance ±0.01 g (common use)



• One tripod stand and wire gauze

• One thermometer 0 °C to 100 °C

• One crucible and lid

• One filter funnel and filter paper




• Oven (common use)

• Magnetic stirrer, one per four candidates

• One 50 cm3 measuring cylinder Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Correct technique of weighing

2. Ensuring that the entire product is removed from the filter paper

3. Ensuring that the temperature of the oven is 120 °C


63

Experiment 18 Topic : Technique − Synthesis Purpose : To prepare and to purify a sample of benzoic acid Materials : KA 1 is liquid benzaldehyde.

KA 2 is hydrated sodium sulphite.

KA 3 is solid anhydrous sodium carbonate.

KA 4 is solid potassium manganate(VII).

KA 5 is 2.0 mol dm-3 hydrochloric acid. Procedure : (a) Weigh out accurately between 2.0 g and 2.5 g of KA 1. Record your readings in the table below.

Place all of KA 1 into a 600 cm3 conical flask. Add approximately 2.5 g of KA 3 followed by 5 g of KA 4. Then add 100 cm3 of distilled water. Shake well, and if necessary warm the mixture until the oily drops of KA 1 disappear. Filter. To the filtrate, add 20 g of KA 2 followed by 100 cm3 of KA 5 a little at a time while shaking the conical flask. Cool, and filter the crystalline precipitate of benzoic acid by means of suction filtration. Place the crude crystalline benzoic acid in a 100 cm3 beaker, and to it add hot water of about 80 °C slowly while stirring the solution until all the crystals dissolve. Leave the solution to cool in the ice-bath. Filter the crystals formed by means of the suction filtration apparatus. Dry and weigh the benzoic acid crystals obtained. Results : (b) Record all your readings in the table below.

Mass of container + KA 1/g


Mass of KA 1/g

Mass of container + benzoic acid/g


Mass of benzoic acid/g

Questions : (c) Write a balanced equation for the oxidation of benzaldehyde to benzoic acid. (d) Calculate the number of moles of KA 1 used in your experiment. (e) Calculate the maximum mass of benzoic acid that may be formed from the number of moles of KA 1 which you used in part (d).


64

(f) Calculate the percentage of benzoic acid produced in your experiment.

(g) How would you ensure whether the benzoic acid crystals obtained are pure? (h) What is the role of hydrated sodium sulphite in this experiment?


65

Notes for Teachers 1. This experiment is conducted in groups.

2. The students are required to submit the product of the experiment together with their reports.

Materials • KA 1 is liquid benzaldehyde, about 2.00 g to 2.50 g per group.

• KA 2 is solid hydrated sodium sulphite, about 40.00 g per group.

• KA 3 is solid anhydrous sodium carbonate, about 2.50 g per group.

• KA 4 is solid potassium manganate(VII), about 5.00 g per group.

• KA 5 is a solution containing 172.0 cm3 of concentrated hydrochloric acid per dm3, about 150 cm3 per group.

• Distilled water, about 150 cm3 per group

• Hot water, about 100 cm3 per group

• Ice cubes Apparatus per group • Electric balance ±0.01 g (common use)



• One tripod stand and wire gauze


• One filter funnel and filter paper


• One Buchner filter funnel and its conical flask

• One thermometer 0 °C to 100 °C

• One wash bottle filled with distilled water Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Correct method employed in weighing

2. Correct method employed in handling the Buchner filtration apparatus

3. Correct technique employed in carrying out the recrystallisation and drying of crystals


66

Experiment 19 Topic : Separation Process − Chromatography

Purpose : To separate and to identify the colours found in a type of commercial food dye

Materials : Food dye Ethanol Procedure : (a) Prepare 100 cm3 of ethanol and water solvent in the ratio of 3:1. Pour this solvent into a 1 dm3 tall container. Cover the mouth of the container with plastic and leave it to stand for 30 minutes.

On a strip of filter paper measuring about 4 cm wide and 38 cm long, mark lightly a line with a pencil about 2 cm from one end. Using a fine glass capillary pipette, spot the solution of food dye onto a marked spot in the middle of the line as shown in the diagram below. Dry the spot with a hair dryer.

Diagram showing method of spotting the sample onto the filter paper Suspend this paper in the tall container with its lower end touching the solvent. Ensure that the pencil line is above the solvent level and the sides of the filter paper do not touch the walls of the high container as shown in the diagram below.

Development chamber for paper chromatography


67

Leave the apparatus to stand for 1 to 2 hours. Then remove this filter paper and mark the position of the solvent front immediately. Dry the paper with a hair dryer.

Obtain the Rf values for each of the spots separated. Measure the distance moved by the solvent front and the distance moved by the colour components from the starting line. Results : (b) Record your results in the table below.

Substance

Component Colour of

component Distance of movement of

component/cm

Distance of solvent

front/cm

Rf

Questions : (c) Using your results from the table above and information given by your teacher, identify the colour components in the sample of food dye provided. (d) In this paper chromatography experiment, state the substance that functions as the (i) stationary phase, (ii) mobile phase. (e) Explain how you would ensure that the drop of food dye at the starting line is concentrated and small in size? (f) Why must the starting line containing the drops of food dye solution be placed above the solvent level at the beginning of the experiment? (g) State the steps taken to ensure effective separation.


68

Notes for Teachers

1. This experiment can be conducted individually or in groups.

2. The teacher is required to carry out the experiment earlier to obtain Rf values of colours to be given to the students. The colours and Rf values obtained are to be used by the students as reference and identification to answer question (b).

The following are several colours that can be obtained from shopping centres.

Rf values for several food dyes

Colour Rf

Amaranth (C.I 16185) Brilliant Blue FCF (C.I. 42090) Allure Red (C.I. 16035) Tartrazine (C.I. 19140) Carmoisine

Sunset Yellow

3. The students are required to submit their chromatograms together with their reports. Materials • Several food dyes, each type of dye containing at least two colour components per

candidate/group

• Ethanol, about 100 cm3 per candidate/group

• Distilled water, about 100 cm3 per candidate/group Apparatus per candidate/group • Tall container or 1000 cm3 measuring cylinder

• Filter paper measuring 6 cm × 16 cm or 4 cm × 55 cm or 6 cm × 20 cm

• Hair dryer

• Plastic to cover the tall container

• Fine glass capillary pipette

• Scissors Skills A, B, C, and E Examples of skills A that can be observed are as follows:

1. Technique employed in the preparation of solvent according to the required ratio

2. Technique employed in the preparation of the chromatography paper

3. Technique employed to spot the food dye solution onto the filter paper

4. Technique employed to suspend the filter paper in the tall cylinder containing the solvent


69

Experiment 20 Topic : Separation Process − Extraction Purpose : To investigate the effect of solvent volume and number of extractions on

the percentage of extracted product Materials : KA 1 is 0.01 mol dm-3 succinic acid.

KA 2 is 0.03 mol dm-3 aqueous sodium hydroxide.

KA 3 is liquid 2-methyl-1-propanol. Phenolphthalein as indicator Procedure : (a) (i) By means of a measuring cylinder, transfer 25.0 cm3 of KA 3 into a 150 cm3 conical flask. Then pipette 25.0 cm3 of KA 1 into this conical flask. Close this conical flask with a stopper and shake vigorously for 10 minutes. Leave the mixture to settle for 5 minutes so that two layers are formed. Then, by means of a pipette, transfer 10.0 cm3 of the organic layer, that is the upper layer, into a titration flask and titrate the solution with KA 2. Use phenolphthalein as indicator. One accurate titration will suffice. Record your readings in the table below.

(ii) Pour the remaining solution mixture from the conical flask above into a separating funnel. Leave it for 5 minutes so that two layers are formed. Run out the bottom layer from the separating funnel into a clean empty conical flask. Pipette 25.0 cm3 of KA 3 into this conical flask and shake vigorously for 10 minutes. Leave the mixture for 5 more minutes so that two layers are formed. By means of a pipette, transfer 10.0 cm3 of the organic layer, that is the upper layer, into the titration flask and titrate the solution with KA 2 using phenolphthalein as indicator. Record your readings in the table below.

(iii) Repeat the same procedure in (a) (i) by using 50 cm3 of KA 3. Record your readings in the table below. Results : (b) Record all your titration readings in the same table below.

Procedure (a)(i) (a)(ii) (a)(iii)

Final reading/cm3

Initial reading/cm3

Volume of KA 2/cm3


70

Questions : (c) Calculate the concentration of succinic acid, in g dm-3, in the organic layer of 2-methyl-1-propanol according to procedure (a) (i) and hence, calculate the mass of succinic acid, in g, in 25 cm3 of extracting solvent 2-methyl-1-propanol. (d) Calculate the concentration of succinic acid, in g dm-3, in the organic layer of 2-methyl-1-propanol according to procedure (a) (ii) and calculate the mass of succinic acid, in g, in another 25 cm3 of extracting solvent 2-methyl-1-propanol. (e) Calculate the mass of succinic acid, in g, in 50 cm3 of extracting solvent 2-methyl-1-propanol. (f) Calculate the concentration of succinic acid, in g dm-3, in the organic layer of 2-methyl-1-propanol according to procedure (a) (iii) and hence calculate the mass of succinic acid, in g, in 50 cm3 of extracting solvent 2-methyl-1-propanol. (g) Using your answers to (c) and (f), explain the influence of varying volumes of extracting solvent upon the effect of the extraction of succinic acid. (h) Using your answers to (d) and (f), compare the efficiency of the extraction in procedures (a) (i) and (a) (ii) with that in procedure (a) (iii). Comment on your answer.


71

Notes for Teachers This experiment is conducted in groups. Materials • KA 1 is a solution containing 11.81 g of succinic acid per dm3, about 70 cm3 per group.

• KA 2 is a solution containing 3.00 g of sodium hydroxide per dm3, about 200 cm3 per group.

• KA 3 is liquid 2-methyl-1-propanol (isobutanol), about 100 cm3 per group.

• Phenolphthalein as indicator Apparatus per group • One 50 cm3 measuring cylinder

• Three 150 cm3 conical flasks and stoppers



• One 10 cm3 pipette



• One 100 cm3−150 cm3 separatory funnel and stopper

• One stopwatch


• One white tile Skills A, B, C, and E Examples of skills A that can be observed are as follows: 1. Correct technique employed in using the separatory funnel

2. Using the indicator at the appropriate time


72

Appendix A Student Record

SIJIL TINGGI PERSEKOLAHAN MALAYSIA (2007/2008 SESSION)

SCHOOL-BASED ASSESSMENT OF PRACTICAL CHEMISTRY (PAPER 962/3)

Name of school/college: ............................................................................................................................

Name of student: .......................................................................................................................................

Identity card number: ................................................ Centre number/index number: .............................

Mark for skill assessed Date Experiment

number A B C D E Notes

Total

Overall total mark

DECLARATION 1

I declare that the marks and information recorded above are true.

Signature of teacher 1: .................................................... Name: .............................................................

Signature of teacher 2: .................................................... Name: .............................................................

Signature of teacher 3: .................................................... Name: ............................................................. DECLARATION 2

I confirm that the above declaration is true.

Signature of Principal: ........................................................... Date: .................................

Official stamp:


73

Appendix B

SIJIL TINGGI PERSEKOLAHAN MALAYSIA (2007/2008 SESSION) SCHOOL-BASED ASSESSMENT FOR PRACTICAL CHEMISTRY (PAPER 962/3)

EXPERIMENT REPORT Name of school/college: ……………………………………………………………………………………… Centre number: ………………………

Experiment Number Topic Problem/Modification/Suggestion/Comment

Note: If there is no problem/modification/suggestion/comment for a certain experiment, please write “NONE”.

Download - Teachers Manual

Top Related