Teachers Manual

SIJIL TINGGI PERSEKOLAHAN MALAYSIA (STPM) (MALAYSIA HIGHER SCHOOL CERTIFICATE)

Teacher’s Manual Practical Chemistry Paper 962/3 (School-based Assessment) Assessment)

CONTENTS Page

1.0

Introduction

1

2.0

Administration of Practical Chemistry Assessment at School

1

3.0

Moderation

4

4.0

Practical Work Assessment Guide

5

5.0

Table of Summary of Experiments

9

6.0

Preparation of Solutions for Volumetric Analysis Analysis

12

Experiment 1

15

Experiment 2

17

Experiment 3

20

Experiment 4

23

Experiment 5

26

CONTENTS Page

1.0

Introduction

1

2.0

Administration of Practical Chemistry Assessment at School

1

3.0

Moderation

4

4.0


5

5.0

Table of Summary of Experiments

9

6.0

Preparation of Solutions for Volumetric Analysis Analysis

12

Experiment 1

15

Experiment 2

17

Experiment 3

20

Experiment 4

23

Experiment 5

26

STPM CHEMISTRY

TEACHER'S MANUAL 2007/2008

SCHOOL-BASED ASSESSMENT OF PRACTICAL CHEMISTRY 1.0

Introduction

1.1

Some of the skills that that should be developed developed in science subjects (e.g. (e.g. handling of apparatus, observation, interpretation of results, and planning) can only be fully acquired through practical work.

1.2

Continuous assessment assessment of of practical work at school throughout form six six will ensure that direct observations of all the desired practical skills and scientific attitudes of students can be made.

1.3

The practical practical science assessment assessment is carried carried out out at school school level level with the following aims. (a)

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

(b)

To improve improve the practical practical skills skills and the quality of practical practical work of students students

(c)

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

STPM CHEMISTRY


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.

STPM CHEMISTRY


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

STPM CHEMISTRY

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.

STPM CHEMISTRY

4.0



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)

STPM CHEMISTRY


(c)

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

4.2.2

3

−

Give TWO marks for the difference between 0.00 cm 3 0.30 cm .

−

Give ONE mark for the difference between 0.31 cm3 and 3 0.50 cm .

−

No mark for the difference greater than 0.50 cm .

and

3

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:

STPM CHEMISTRY


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)

4.3.2

Graph (2 marks) −

Give ONE mark for axes labelled, and with the correct units.

−

Give ONE mark for the correct shape of the graph.

Technique (Qualitative Analysis)

(a)

Filling the ‘deduction’ space correctly. (5 marks) Minus ONE mark for each incorrect deduction.

STPM CHEMISTRY

4.5


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)

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

STPM CHEMISTRY


5.0 Table of Summary of Experiments

Experiment

Topic

1*

Volumetric analysis

Subtopic

Mode of working

Report to be completed

Skills tested

Purpose

Time

Acid base

To determine the exact concentration of a mineral acid, H X O4 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

Individually

In the laboratory

A, B, C, E

3*

Acid base and

To determine the

1½

In groups

In the

A, B,

STPM CHEMISTRY



Skills tested

Experiment

Topic

Subtopic

Purpose

Time

Mode of working

10*

Physical Quantity

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, K sp of lead(II) iodide

1½ hours

Individually

In the laboratory

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


In the laboratory

A, B, C, E

13*

Electrochemistry - Faraday's Laws

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

1½ hours

Individually

In the laboratory

A, B, D, E

Qualitative analysis

To determine the cations and anions of

1½ hours

Individually

In the laboratory

A, B, C, D,

14*

Technique

STPM CHEMISTRY



Experiment

Topic

Subtopic

Purpose

Time

Mode of working

19*

Technique

Separation process Chromatography

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

2½ hours


At home

A, B, C, E

Separation process Extraction

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

2 hours

In groups

At home

A, B, C, E

20*

* Compulsory experiment to be carried out for assessment.

Skills tested

STPM CHEMISTRY

6.0


Preparation of Solutions for Volumetric Analysis -3

For a 0.05 mol dm solution of sodium ethanedioate, Na 2C2O4, with a relative formula -3 mass of 134.0, its concentration in g dm 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 =

mass and the specifications given in the table volume

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

Acid

Relative Molecular Mass

Density or Specific Gravity

Purity

STPM CHEMISTRY


Step 2

For more accurate work, these solutions need to be standardised using a standard solution of sodium carbonate, Na 2CO3. 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 -3 moisture. The substance is then cooled in a desiccator. The amount required (5.3 g dm 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, Na 2S2O3.5H2O, (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

STPM CHEMISTRY

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 cm 3 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

22.4 68

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 -3

20 22.4

´ 68 = 60.8g. 3

Therefore, to prepare a 0.1 mol dm solution of H2O2, about 5.6 cm of 20-volume hydrogen peroxide must be diluted to make 1 litre. Other

STPM CHEMISTRY


Experiment 1 Topic

:

Volumetric analysis − Acid base

Purpose

:

To determine the exact concentration of a mineral acid, H X O4, and to determine the relative atomic mass of the element X

Materials

:

KA 1 is a mineral acid, H X O4. −

3

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

Phenolphthalein as indicator.

Procedure :

3

(a) Pipette 25.0 cm 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.

STPM CHEMISTRY


Notes for Teachers Materials •

KA 1 is a solution containing 8.6 cm 3 of concentrated hydrochloric acid per dm 3, -3 3 (0.10 mol dm ), about 100 cm per candidate.

•

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

•

Phenolphthalein as an indicator

3

Apparatus per candidate 3

•

One 25 cm pipette and pipette filler

•

Three titration flasks

•

One 50 cm burette

•

One retort stand and clamp

•

One white tile

3

-3

STPM CHEMISTRY


Experiment 2 Topic

:

Purpose

:

Materials

:

Volumetric analysis − 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 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 3 sulphate, (NH3OH)2SO4 per dm 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, NH 3OH + will reduce iron(III) ion to iron(II) ion while the NH3OH ion itself will be oxidised to dinitrogen oxide.

Procedure

:

3

(a) Pipette 25.0 cm of KA 2 into a titration flask. Add approximately

STPM CHEMISTRY


( 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 Fe (h) Why would the titration not require an external indicator?

3+

ions.

STPM CHEMISTRY



KA 1 is a solution containing 3.16 g of potassium manganate(VII) per dm 3, about 3 200 cm per candidate.

•

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

•

KA 3 is a solution containing 54.9 cm 3 of concentrated sulphuric acid per dm 3, about 3 200 cm per candidate.

Apparatus per candidate •

One 25 cm3 pipette and pipette filler

•


•

One 50 cm burette

3

STPM CHEMISTRY


Experiment 3 Topic

:

Purpose

:

Materials

:

Volumetric analysis − Acid base and redox

To determine the mass of sodium ethanedioate used to prepare a solution containing sodium ethanedioate and hydrated ethanedioic acid KA 1 is a solution containing hydrated ethanedioic acid, H 2C2O4.2H2O, and sodium ethanedioate. KA 2 is a solution containing 3.5 g potassium manganate(VII) per dm 3. KA 3 is a solution containing 1.7 g hydroxyl ions per dm 3. KA 4 is 1.0 mol dm-3 sulphuric acid.

Phenolphthalein as indicator

Procedure :

3

(a) Pipette 25.0 cm 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. Repeat the titration as many times as you think necessary to achieve accurate results.

STPM CHEMISTRY

Results

:


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

Titration

Accurate

Rough

3

Final reading/cm

3

Initial reading/cm

Volume of KA 2 /cm3 3

3

(i) 25.0 cm of KA 1 required ……… cm of KA 2 for a complete reaction. (ii) Calculate your average average titre value value showing the the suitable titre values that you use.

Questions

: -3

(e) Calculate the concentration, in mol dm , of hydrated ethanedioic acid in solution KA 1.

STPM CHEMISTRY


Notes for Teachers This experiment is to be conducted in pairs.

Materials •

KA 1 is a solution containing 3.0 g of sodium ethanedioate, Na 2C2O4, and 4.0 g 3 3 hydrated ethanedioic acid, H 2C2O4.2H2O, per dm , about 250 cm per candidate.

•

KA 2 is a solution containing 3.50 g potasium manganate(VII), KMnO 4, per dm , 3 about 120 cm per candidate.

•

KA 3 is a solution containing 4.00 g sodium hydroxide per dm 3, about 120 cm 3 per candidate.

•

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

•


3

Apparatus per group (2 candidates) •

3

Two 25 cm pipettes and pipette fillers 3

Two 50 cm burettes

STPM CHEMISTRY


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 aqueous iodine.

-3

-3

KA 2 is 0.1 mol dm aqueous sodium thiosulphate. KA 3 is a solution containing 24.0 g of anhydrous sodium sulphite, 3 Na2 SO3, per dm . 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

−

SO4 2

+ I2 + H2O

2HI + 2HCO3

−

2I

−

−

+ 2HI

+ 2H2O + 2CO2

If a solution of sodium sulphite is added to an excess of a standard solution of iodine, the

STPM CHEMISTRY

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 I 2 that reacted with the sulphite ions. ( f ) Using your answer to (e), -3

(i) calculate the concentration, in mol dm , of the sulphite ions in solution KA 3, 3 (ii) calculate the mass of Na2SO3 present in 250 cm of KA 3.

(g) Using your answer to ( f )(ii), calculate the percentage purity of Na2SO3 that you used.

STPM CHEMISTRY



KA 1 is a 0.025 mol dm -3 aqueous iodine prepared by dissolving 6.35 g of solid iodine 3 3 in 10% solution of potassium iodide per dm , about 250 cm per candidate.

•

KA 2 is a solution containing 12.41 g of sodium thiosulphate per dm , about 200 cm per candidate.

•

KA 3 is a solution containing 3.15 g of anhydrous sodium sulphite, Na 2SO3, per dm3, 3 about 150 cm per candidate.

•

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

•

Starch as indicator

3


•


•

One 50 cm3 pipette

3

STPM CHEMISTRY


Experiment 5 Topic

:

Volumetric analysis − stoichiometry

Purpose

:

To determine the exact concentration of a monobasic acid, H X

Question

:

You are provided with a monobasic acid, H X , with a concentration in -3 -3 the range of 0.5 mol dm to 1.0 mol dm . You are required to plan and carry out an experiment to determine the exact concentration of the H X solution provided.

STPM CHEMISTRY


Notes for Teachers This experiment is to be conducted after the teacher has taught the topic on Ionic Equilibrium.

Materials 3

•

A suitable monobasic acid is hydrochloric or ethanoic acid, about 150 cm 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 cm per candidate.

3


•

250 cm volumetric flask and stopper

•

Electric balance ±0.01 g or equivalent (common use) 3

One 25.0 cm pipette and pipette filler

per

STPM CHEMISTRY


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 hydrochloric acid.

-3

-3

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

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

KA 4 is 1.0 mol dm nitric acid. -3

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

Procedure :

3

By means of a measuring cylinder, add 30 cm 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.

STPM CHEMISTRY

Questions


: 3

(c) If 4.2 Joules is required to raise the temperature by 1 °C for 1 cm 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

STPM CHEMISTRY



KA 1 is a solution containing 86.0 cm 3 of concentrated hydrochloric acid per dm 3, 3 about 20 cm per candidate.

•

KA 2 is a solution containing 54.0 cm of concentrated sulphuric acid per dm , about 20 3 cm per candidate.

•

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

•

KA 4 is a solution containing 65.0 cm 3 of concentrated nitric acid per dm 3, about 3 cm per candidate.

•

KA 5 is a solution containing 56.0 g of potassium hydroxide per dm , about 50 cm per candidate.

3

3


3

3


20 3

STPM CHEMISTRY


Experiment 7 Topic

:

Thermochemistry

Purpose

:

To determine the heat of reaction

Materials

:


-3

KA 2 is solid anhydrous sodium carbonate. KA 3 is solid sodium hydrogen carbonate. 3 (a) Using a burette, run 30.00 cm 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.

Procedure :

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

STPM CHEMISTRY


(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 Δ H for the conversion reaction of sodium hydrogen carbonate to sodium carbonate using Hess Law and ( e).

STPM CHEMISTRY


Notes For Teachers Materials •

KA 1 is a solution containing 172 cm 3 of concentrated hydrochloric acid per dm 3, about 3 100 cm 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.


One 50 cm3 burette

•


•

One plastic/polystyrene cup

•

One thermometer 0 °C–110 °C (±0.2 °C) One wash bottle filled with distilled water

STPM CHEMISTRY


Experiment 8 Topic

:

Reaction kinetics

Purpose

:

To determine the effect of temperature on the reaction rate

Materials

:

KA 1 is 0.15 mol dm aqueous potassium iodide.

-3

KA 2 is 0.5% starch solution. -3

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

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

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

Procedure :

3

3

Using a measuring cylinder, place 50 cm of KA 4 and 20 cm of KA 5 into a beaker. Pour the whole solution quickly from this beaker to the contents in the conical

STPM CHEMISTRY

Questions


: (c) Plot a graph of

1 t

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.

STPM CHEMISTRY



KA 1 is a solution containing 24.9 g of potassium iodide per dm 3, about 150 cm3 per candidate.

•

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

•

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

•

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

•

KA 5 is a solution containing 54.0 cm 3 of concentrated sulphuric acid per dm 3, about 3 150 cm per candidate.

•

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

•

Distilled water, about 150 cm per candidate.

3

3

Apparatus per candidate

3

3

STPM CHEMISTRY


Experiment 9 Topic

:

Reaction kinetics

Purpose

:

To investigate the hydrolysis of methyl ethanoate

Materials

:


-3

-3

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

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

Procedure :

3

3

Then pipette immediately 5.0 cm of solution from this 250 cm 3 3 conical flask and transfer the sample to a 250 cm titration flask containing 100 cm of ice water. Note the time when half of the sample in the pipette has been transferred. When all of 3 the 5.0 cm is transferred, add one or two drops of phenolphthalein and titrate this solution

STPM CHEMISTRY

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. 3

(h) Why was the sample of reaction mixture added to 100 cm of ice water before titration? (i) Using the same axes as in ( g), sketch an expected graph for the -3 hydrolysis of the ester conducted at the same temperature but with 0.1 mol dm 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.

STPM CHEMISTRY



KA 1 is hydrochloric acid, 0.5 mol dm -3, about 250 cm 3 per candidate.

•

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

•

KA 3 is methyl ethanoate, about 10 cm per candidate.

•


•

Ice water, about 600 cm per candidate

•

Distilled water, about 150 cm per candidate

3

3

3


•

One 50 cm burette

•


•

Three 250 cm titration flasks

3

3

One 10 cm graduated pipette and pipette filler

STPM CHEMISTRY


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 solution of a weak acid.

Procedure :

-3

3

3

(a) Prepare four 100 cm beakers labelled W , X , Y , and Z . Pipette 20.0 cm 3 of KA 1 into beaker W . Then pipette 2.0 cm of KA 1 from beaker W into beaker X . Run 3 3 18.00 cm of distilled water from the burette into beaker X . Stir the solution. Pipette 2.0 cm 3 of the solution from beaker X into beaker Y . Add 18.0 cm of distilled water into beaker Y . 3 Repeat the same procedure for beaker Z using 2.0 cm 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. 3

3

(Note: The final volume in beakers W , X , and Y is 18.0 cm whereas it is 20.0 cm in beaker Z .)

STPM CHEMISTRY


Notes for Teachers The teacher is advised to calibrate the pH meter with the standard buffer solution before carrying out the experiment.

Materials 3

3

•

KA 1 is a solution containing 5.7 cm of ethanoic acid (99.5%) per dm , about 30 cm per candidate.

•


3

Apparatus per candidate/group •

pH meter

•

Four 100 cm beakers

•

Four pieces of paper label

•


•

One 1 cm3 graduated pipette

3

3

3

STPM CHEMISTRY


Experiment 11 Topic

:

Equilibrium and solubility

Purpose

:

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

Materials

:

KA 1 is 0.25 mol dm aqueous lead(II) nitrate.

-3 -3

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



KA 5 is 0.01 mol dm 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, K sp, for such systems can be obtained by taking into account the concentration of the ions of solutes in saturated solutions.

Procedure

:

3 (a) Titrate 25.0 cm of KA 1 with KA 5. The end point is achieved when

STPM CHEMISTRY

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 ] 2+

- 2

[Pb ][I ]

(d ) Sketch a graph of [Pb2+][I-]2 against [Pb2+]. (e) Comment on the values of the ionic product of PbI 2. ( f ) Calculate an average value for the solubility product of lead(II) iodide.

STPM CHEMISTRY



KA 1 is a solution containing 82.75 g of lead(II) nitrate per dm 3, about 50 cm 3 per candidate.

•


•


•


•

KA 5 is a solution containing 1.66 g of potassium iodide per dm , about 100 cm per candidate.

3


•

One 50 cm burette

•


3

STPM CHEMISTRY


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. KA 3 is 1.0 mol dm-3 aqueous zinc sulphate. KA 4 is 0.1 mol dm-3 aqueous zinc sulphate. KA 5 is 0.01 mol dm-3 aqueous zinc sulphate. KA 6 is 0.001 mol dm -3 aqueous zinc sulphate.

A saturated solution of potassium chloride (a) By means of measuring cylinders, fill beaker A with 50.0 cm3 of KA 1 3 and beaker B with 50 cm 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

Procedure :

STPM CHEMISTRY


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. θ

Calculate E cell using the following formula. θ

E cell

Results

:

x

=

Length of potentiometer wire

×2V

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

Experiment

Beaker A

Beaker B

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

3

50 cm3 KA 6

KA 1

Length of θ E cell /V wire x /cm

2+

[Zn ]/ -3 mol dm

2+

lg [Zn ]

STPM CHEMISTRY


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 3

3

•

KA 1 is a solution containing 249.5 g of CuSO 4.5H2O per dm , about 100 cm per candidate.

•

KA 2 is a solution containing 574.8 g of ZnSO 4.7H2O per dm3, about 100 cm3 per candidate.

•


•


•


•

KA 6 is a solution containing 0.29 g of ZnSO 4.7H2O per dm , about 100 cm per candidate.

3

3

STPM CHEMISTRY



Five strips of filter paper about 15 cm

•

One zinc plate 7 cm

•

One copper plate 7 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 cm /150 cm beakers

•

One piece of sandpaper

•

One wash bottle filled with distilled water

3

Skills A, B, C, and E

×

×

1 cm

2 cm ×

2 cm

3

STPM CHEMISTRY


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.

STPM CHEMISTRY


Notes for Teachers Materials 3

3

•

Solution containing 250 g of CuSO4.5H2O per dm , about 300 cm per candidate

•

Propanone, about 100 cm 3 per candidate

•


3


One 100 cm3 measuring cylinder

•

One 250 cm beaker

•

Two pieces of copper plates measuring 5 cm

•

Five connecting wires with crocodile clips

•

One ammeter, 0 A-3 A

•

One rheostat, 11

•

One switch

3

Ω

×

4 cm × 0.2 cm

STPM CHEMISTRY


Experiment 14 Topic

:


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

STPM CHEMISTRY


Tests on KA 2 Test

Observation

Deduction

STPM CHEMISTRY


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)

•

-3

Aqueous solution of iron(III) chloride, approximately 50 g dm 3 Dissolve 135 g of solid iron(III) chloride in distilled water containing 20 cm of 3 concentrated hydrochloric acid and make up the volume of solution to 1 dm . -3

•

Aqueous solution of ammonium chloride, approximately 50 g dm

•

Aqueous solution of silver nitrate, approximately 50 g dm

-3

STPM CHEMISTRY


Experiment 15 Topic

:


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 Test

Observation

Deduction

STPM CHEMISTRY


Tests on KA 2 Test

Observation

Deduction

STPM CHEMISTRY



KA 1 is a mixture of solids Al 2(SO4)3 and (NH4)2SO4

•

KA 2 is a mixture of solids KI and KNO3

•


•


•

Devarda's alloy

•

Aqueous solution of potassium iodide, about 50 g dm

•

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

•

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

•

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

•

Aqueous solution of sodium carbonate, about 50 g dm

•

Aqueous lead(II) nitrate, about 50 g dm

•

Other reagents to test for iodide and nitrate ions

-3

-3

-3

-3

-3

STPM CHEMISTRY


Experiment 16 Topic

:


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

STPM CHEMISTRY


Tests on KA 2 Test

Observation

(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. 3

3

(i) Add 1 cm to 2 cm 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

Deduction

STPM CHEMISTRY



KA 1 is 5 cm3 of liquid aniline (phenylamine).

•

KA 2 is solid salicylic acid.

•


•


•

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 3 Dissolve 135 g of solid iron(III) chloride in distilled water containing 20 cm of 3 concentrated hydrochloric acid and make up the volume of the solution to 1 dm .

•

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 °

STPM CHEMISTRY


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. -3

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

KA 4 is 2 mol dm 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.

STPM CHEMISTRY

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?

STPM CHEMISTRY



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

•

KA 2 is a solution containing 154 g of CH 3COONH4 per dm3, about 100 cm 3 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 cm of concentrated hydrochloric acid per dm , about 10 cm3 per group.

•

Distilled water, about 200 cm per group

•

Ice cubes

3

3

Apparatus per group

3

STPM CHEMISTRY


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). -3


Procedure :

(a) Weigh out accurately between 2.0 g and 2.5 g of KA 1. Record your readings in the table below. 3

Place all of KA 1 into a 600 cm conical flask. Add approximately 3 2.5 g of KA 3 followed by 5 g of KA 4. Then add 100 cm of distilled water. Shake well, and if necessary warm the mixture until the oily drops of KA 1 disappear. Filter. To the filtrate, 3 add 20 g of KA 2 followed by 100 cm of KA 5 a little at a time while shaking the conical

STPM CHEMISTRY


( 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?

STPM CHEMISTRY



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 cm 3 of concentrated hydrochloric acid per dm 3, 3 about 150 cm per group.

•

Distilled water, about 150 cm per group

•

Hot water, about 100 cm per group

•

Ice cubes

3

3

STPM CHEMISTRY


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 :

3

(a) Prepare 100 cm of ethanol and water solvent in the ratio of 3:1. Pour 3 this solvent into a 1 dm 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.

STPM CHEMISTRY


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.

STPM CHEMISTRY



This experiment can be conducted individually or in groups.

2.

The teacher is required to carry out the experiment earlier to obtain R f values of colours to be given to the students. The colours and R f 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.

STPM CHEMISTRY


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

3 (a) (i) By means of a measuring cylinder, transfer 25.0 cm of KA 3 3 3 into a 150 cm conical flask. Then pipette 25.0 cm 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 3 for 5 minutes so that two layers are formed. Then, by means of a pipette, transfer 10.0 cm 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.

Procedure :

STPM CHEMISTRY

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 3 succinic acid, in g, in 25 cm of extracting solvent 2-methyl-1-propanol. -3

(d ) Calculate the concentration of succinic acid, in g dm , in the organic layer of 2-methyl-1-propanol according to procedure ( a) (ii) and calculate the mass of 3 succinic acid, in g, in another 25 cm of extracting solvent 2-methyl-1-propanol. (e) Calculate the mass of succinic acid, in g, in 50 cm solvent 2-methyl-1-propanol.

3

of extracting

-3

( f ) Calculate the concentration of succinic acid, in g dm , in the organic layer of 2-methyl-1-propanol according to procedure ( a) (iii) and hence calculate the mass of 3 succinic acid, in g, in 50 cm 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

STPM CHEMISTRY


Notes for Teachers This experiment is conducted in groups.

Materials •

KA 1 is a solution containing 11.81 g of succinic acid per dm 3, about 70 cm3 per group.

•

KA 2 is a solution containing 3.00 g of sodium hydroxide per dm 3, about 200 cm 3 per group.

•

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

•


Apparatus per group 3

•

One 50 cm measuring cylinder

•

Three 150 cm conical flasks and stoppers

•


•

One 25 cm3 pipette and pipette filler

•

One 10 cm pipette

3

3

STPM CHEMISTRY


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: ............................. Date

Experiment number

Mark for skill assessed A

B

C

D

E

Notes

Teachers Manual

Recommend Documents