sp 2007(3-5)

Centre Number Candidate Number Name

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS

General Certificate of Education

Advanced Subsidiary Level and Advanced Level

CHEMISTRY 9701/31

Paper 31 Advanced Practical Skills

For Examination from 2007

SPECIMEN PAPER 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in Instructions to Supervisors.

READ THESE INSTRUCTIONS FIRST

Write your Centre number, candidate number and name on all the work you hand in. Give details of the practical session and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. You are advised to show all working in calculations. Use of a Data Booklet is unnecessary. Qualitative Analysis Notes are printed on pages 9 and 10. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

Session

Laboratory

For Examiner’s Use

1

2

TOTAL

This document consists of 10 printed pages.

UCLES 2006 [Turn over

www.XtremePapers.com

2

UCLES 2006 9701/31/SP07

For

Examiner's

Use

1 FA 1 is 2.00 mol dm-3 sodium hydroxide, NaOH.

FA 2 is approximately 0.75 mol dm-3 sulphuric acid, H2SO4. A student suggests that the concentration of the sulphuric acid can be determined by measuring the temperature of the solution as the acid is added in small amounts to a known volume of FA 1 in a plastic cup. The student proposes the following hypothesis. As the acid is added to the alkali the temperature rise will be directly proportional to the volume of acid added until the end-point of the reaction is reached. Upon further addition of acid there will be a reduction in the temperature of the solution in the cup as the acid added is not reacting and is at a lower temperature than the solution in the plastic cup.

2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)

(a) Use the equation for the reaction to estimate the volume of approximately 0.75 mol dm-3 H2SO4 that will neutralise 25.0 cm3 of 2.00 mol dm-3 NaOH.

[1]

(b) In the experiment you will add FA2 from the burette to 25.0 cm3 of FA1 in a plastic cup. You will measure the temperature of the solution after each addition of acid. You will be required to plot a graph of the temperature before and after the end-point in order to determine the end-point accurately and consequently calculate the precise concentration of H2SO4 in FA2.

In order to obtain precise information about the end-point of the reaction, you will need to decide

how many additions of H2SO4 are to be made, the volume of acid to be added each time.

number of additions of H2SO4

volume of acid added each time [2]

3

© UCLES 2006 9701/31/SP07 [Turn over

For

Examiner's

Use (c) In the space below you should record the results of your experiment, including the initial temperature of FA 1 in the plastic cup when no acid has been added, the total volume of FA 2 added at each stage of the experiment, the temperature of the solution in the plastic cup after each addition of acid,

the temperature rise, ∆T.

[∆T = temperature of the solution after each addition of acid – initial temperature of FA 1] [5]

You must decide how best to record and present your measurements. [3]

Results

Experimental procedure: Fill the burette with FA 2. Support the plastic cup in the 250 cm3 beaker and pipette 25.0 cm3 of FA 1 into the plastic cup. Measure and record the steady temperature of FA 1. Run into the cup the first volume of FA2 you have selected, stir and record the highest temperature observed. Immediately add a second volume of FA2 from the burette and repeat the temperature measurement. Continue until you have added all of the planned volume of FA2.

4

UCLES 2006 9701/31/SP07

For

Examiner's

Use

(d) Plot a graph of ∆T against volume of FA 2 added.

Draw two distinct and intersecting lines, one for the increasing and one for the decreasing temperatures.

[4]

(e) The lines intersect at cm3 of H2SO4. [1]

5


For

Examiner's

Use

(f) Use the results of your experiment to calculate the exact concentration of H2SO4. Show all your working and explain the steps in your calculation.

[2] (g) Explain how the results of your experiment support or do not support each part of the

hypothesis proposed by the student.

[3]

(h) From the points plotted and the shape of your graph suggest and explain a possible

error in the measurements taken in this experiment.

[2]

(i) From what you know about the accuracy of your apparatus, calculate the % error in the volume of acid added at the end-point.

[1]

(j) Another student puts forward the hypothesis that the heat energy produced in the reaction, rather than the temperature rise, is proportional to the volume of acid added.

How could the data collected in the experiment be converted into heat energy produced?

[4.3 J raises the temperature of 1 cm3 of solution by 1 oC] [1]

6

UCLES 2006 9701/31/SP07

For

Examiner's

Use

2 Labels have become detached from two bottles of chemicals, each containing a white

powder. One of these is believed to be barium iodide and the other a metal nitrate. A solution has been prepared from each of the solids and these solutions are labelled FA 3 and FA 4.

(a) By selecting a suitable reagent from those listed in the reactions of anions on page 10,

you should carry out a test to establish which of the solutions contains the iodide ion.

Record details of the test performed and the observations obtained in the test in the space below.

From this test, solution FA ……. contains the iodide ion. [2]

(b) By selecting another suitable reagent, carry out a test on the solution you have chosen,

to confirm the presence of the iodide ion.

Record details of the test performed and the observations obtained in the test in the space below. State, with reasons, whether or not this confirms your choice above.

[2] You are to perform the tests given in the table opposite on each of FA 3 and FA 4 to (i) confirm the presence of the nitrate ion in the solution not chosen above, (ii) identify and confirm the cation in each solution.

Record details of colour changes seen, the formation of any precipitate and the

solubility of any such precipitate in an excess of the reagent added. Where gases are released they should be identified by an appropriate test which

you should describe in your observations. You should indicate clearly at what stage in a test a change occurs. Marks are not given for chemical equations. No additional tests for ions present should be attempted. [6]

7


For

Examiner's

Use

test observations with FA3 observations with FA4

(c) To 1 cm depth of solution in a boiling-tube, add aqueous sodium hydroxide drop-wise until it is in excess; then

add a piece of aluminium foil and warm the tube. Care – solutions containing sodium hydroxide can “bump” when heated and eject the hot alkali from the tube.

(d) To a 1cm depth of solution in a test-tube, add aqueous ammonia drop-wise until it is in excess.

(e) To 3 cm depth of solution in a test-tube, add 2 cm depth of dilute sulphuric acid.

(f) To 3 cm depth of solution in a test-tube, add 2 cm depth of aqueous potassium chromate(VI); then

add 2 cm depth of dilute hydrochloric acid.

8

UCLES 2006 9701/31/SP07

For

Examiner's

Use

(g) Explain how your observations identify and confirm the presence of barium ions in the

solution that contained the iodide ion.

[1]

The observations made with aqueous sodium hydroxide and aqueous ammonia should have indicated either of two possible cations in the other solution.

Identify these cations; explain the observations and explain how other tests carried out

eliminate one of these cations.

[2]

(h) The test that indicates the presence of a nitrate would also give a positive result with

nitrite. Suggest a test to distinguish between these two ions. Do not carry out this test.

[1]

9


Qualitative Analysis Notes

Key: [ ppt. = precipitate. ] 1 Reactions of aqueous cations

reaction with

NaOH(aq) NH3(aq)

aluminium,

Al3+(aq)

white ppt.

soluble in excess

white ppt.

insoluble in excess

ammonium,

NH4+(aq)

ammonia produced on heating

barium,

Ba2+(aq)

no ppt. (if reagents are pure) no ppt.

calcium,

Ca2+(aq)

white ppt. with high [Ca2+(aq)] no ppt.

chromium(III),

Cr3+(aq)

grey-green ppt. soluble in excess

giving dark green solution

grey-green ppt.

insoluble in excess

copper(II),

Cu2+(aq)

pale blue ppt.

insoluble in excess

blue ppt. soluble in

excess

iron(II),

Fe2+(aq)

green ppt.

insoluble in excess

green ppt.

insoluble in excess

iron(III),

Fe3+(aq)

red-brown ppt.

insoluble in excess

red-brown ppt.

insoluble in excess

lead(II),

Pb2+(aq)

white ppt.

soluble in excess

white ppt.

insoluble in excess

magnesium,

Mg2+(aq)

white ppt.

insoluble in excess

white ppt.

insoluble in excess

manganese(II),

Mn2+(aq)

off-white ppt.

insoluble in excess

off-white ppt.

insoluble in excess

zinc,

Zn2+(aq)

white ppt.

soluble in excess

white ppt.

soluble in excess

[Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.]

10

UCLES 2006 9701/31/SP07

2 Reactions of anions

ion reaction

carbonate,

CO32-

CO2 liberated by dilute acids

chromate(VI),

CrO42- (aq)

yellow solution turns orange with H+(aq);

gives yellow ppt. with Ba2+(aq);

gives bright yellow ppt. with Pb2+(aq)

chloride,

Cl - (aq)

gives white ppt. with Ag+(aq) (soluble in NH3(aq));

gives white ppt. with Pb2+(aq)

bromide,

Br- (aq)

gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq));

gives white ppt. with Pb2+(aq)

iodide,

I- (aq)

gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq));

gives yellow ppt. with Pb2+(aq)

nitrate,

NO3- (aq)

NH3 liberated on heating with OH-(aq) and Al foil

nitrite,

NO2- (aq)

NH3 liberated on heating with OH-(aq) and Al foil,

NO liberated by dilute acids

(colourless NO → (pale) brown NO2 in air)

sulphate,

SO42- (aq)

gives white ppt. with Ba2+(aq) or with Pb2+(aq) (insoluble in excess dilute strong acids)

sulphite,

SO32- (aq)

SO2 liberated with dilute acids;

gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids)

3 Tests for gases

gas test and test result

ammonia, NH3 turns damp red litmus paper blue

carbon dioxide, CO2 gives a white ppt. with limewater

(ppt. dissolves with excess CO2)

chlorine, Cl2 bleaches damp litmus paper

hydrogen, H2 “pops” with a lighted splint

oxygen, O2 relights a glowing splint

sulphur dioxide, SO2 turns potassium dichromate(VI) (aq) from orange to green

Copyright Acknowledgements:

Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.




CHEMISTRY 9701/31

Paper 31 Practical Test


SPECIMEN CONFIDENTIAL INSTRUCTIONS

Great care should be taken to ensure that any information given does not reach the

candidates either directly or indirectly.


1 Access to the examination paper is not permitted before the examination.

Supervisors are asked to carry out any confirmatory tests included in these instructions to ensure the materials supplied are appropriate. The ‘General Apparatus’ requirements and the ‘Particular Requirements’ are printed separately. It is especially important that the details on page 4 are kept secure.

2 Supervisors are advised to remind candidates that all substances in the examination should be treated with caution. Only those tests described in the question paper should be attempted. Please also see under ‘General Apparatus’ on the use of pipette fillers and safety goggles.

In accordance with COSHH (Control of Substances Hazardous to Health) Regulations, operative in the UK, a hazard appraisal of the examination has been carried out.

Attention is drawn, in particular, to certain materials used in the examination. The following codes are used where relevant. C = corrosive substance F = highly flammable substance

H = harmful or irritating substance O = oxidising substance

T = toxic substance

The Supervisor’s attention is drawn to the form on page 7 which must be completed and returned with the scripts.

If you have any problems or queries regarding these instructions, please contact CIE by e-mail: [email protected]

by phone: +44 1223 553554

by fax: +44 1223 553558

stating the Centre number, the nature of the query and the syllabus number quoted above.

This document consists of 8 printed pages.


2

UCLES 2006 9701/31/SP07

Safety

The attention of Supervisors is drawn to any local regulations relating to safety and first-aid. ‘Hazard Data Sheets’, relating to materials used in this examination, should be available from your chemical supplier.

General Apparatus and Materials

1 In addition to the fittings and reagents ordinarily contained in a chemical laboratory, the apparatus

and materials specified below will be necessary. 2 Pipette fillers and safety goggles should be used where necessary.

3 It is assumed that common bench reagents and reagents/materials for testing gases listed in

the syllabus are available.

[H] 2 mol dm-3 hydrochloric acid [C] 2 mol dm-3 sodium hydroxide [C] 2 mol dm-3 nitric acid [H] 2 mol dm-3 aqueous ammonia [H] 1 mol dm-3 sulphuric acid

[T] 0.1 mol dm-3 potassium chromate(VI) limewater (a saturated solution of calcium

wooden splints hydroxide) and the associated apparatus red and blue litmus indicator papers

For each candidate

1 x plastic cup (expanded polystyrene/foamed plastic) 1 x 250 cm3 beaker (to support the plastic cup) 1 x 50 cm3 burette 1 x stand and burette clamp 1 x small funnel for filling burette 1 x 25 cm3 pipette 1 x pipette filler 1 x thermometer, -10 oC to 110 oC by 1 oC 6 test-tubes 1 boiling-tube 1 x test-tube rack 1 x Bunsen burner 1 x heat proof mat 2 x teat/squeeze pipettes paper towels

Particular Requirements

1 As a possible aid to maintaining security, the descriptions of the particular chemicals required are

given under two headings:

(a) overall specifications are given on page 3;

(b) the actual identities are given on page 4. 2 Materials with an FA code number should be so labelled for the candidates’ benefit, without the

identities being included on the label - where appropriate, the identity of an FA coded chemical is given in the question paper itself.

3


Chemicals Required

1 The chemicals required per question are described in general terms below.

2 Where quantities are specified for each candidate, they are sufficient for the experiments described in the question paper to be completed.

In preparing materials, the bulk quantity for each substance should be increased by 25% as spare material should be available to cover accidental loss.

More material may be supplied if requested by candidates, without penalty. 3 The additional qualitative analysis reagents needed for Question 2 are identified on page 4. 4 For Question 1

[C] Solution FA 1 50 cm3

FA 1 should be supplied in stoppered bottles or in beakers covered with “cling-film” or “gladwrap”.

[H] Solution FA 2 70 cm3

For Question 2

[H] Solution FA 3 30 cm3

[T] Solution FA 4 30 cm3

4

UCLES 2006 9701/31/SP07

Detailed Identities of Chemicals Required

1 It is especially important that great care is taken that the confidential information given below does

not reach the candidates either directly or indirectly. 2 The identities of the chemicals with an FA code number are as follows.

Question 1

[C] FA 1 is 2.00 mol dm-3 sodium hydroxide, NaOH, containing 80.00 g dm-3 of NaOH. This solution should be kept covered before and after issue to candidates to prevent absorption of carbon dioxide from the atmosphere.

[H] FA 2 is 0.75 mol dm-3 sulphuric acid, H2SO4. Prepare this solution by carefully adding 41.0 cm3

of concentrated (95%) sulphuric acid to distilled water and diluting the resulting solution to 1 dm3. The concentration of FA 1 should be checked by titrating a 25.0 cm3 portion of FA 2 against

FA 1. Adjust the concentration of FA 2 to give a titre of 18.75 ± 0.20 cm3. It is essential that the FA 1 solution is kept securely stoppered until the time of the examination to prevent absorption of carbon dioxide. It should be issued to candidates just before the start of the examination – see p3.

Solutions FA 1 and FA 2 should be prepared at least 24 hours before the examination and allowed to stand in the laboratory to equalise their temperature.

[H] FA 3 is 0.1 mol dm-3 aluminium nitrate containing 37.5 g of Al(NO3)3.9H2O in each dm3 of solution.

[T] FA 4 contains 0.1 mol dm-3 barium chloride and 0.1 mol dm-3 potassium iodide. Dissolve 24.5 g

of BaCl2.2H2O and 16.6 g of KI in distilled water and make up to 1 dm3.

3 In addition to those listed on page 2, the qualitative analysis reagents specifically required are set out

below. If necessary, they may be made available from a communal supply: however, the attention of the Invigilators should be drawn to the fact that such an arrangement may enhance the opportunity for malpractice between candidates

aluminium foil

[C] 0.05 mol dm-3 silver nitrate, AgNO3, 8.5 g dm-3

[T] 0.10 mol dm-3 lead(II) nitrate, Pb(NO3)2, 33.0 g dm-3

5


COLOUR BLINDNESS

With regard to colour-blindness – a minor handicap, relatively common in males – it is permissible to advise candidates who request assistance on colours of, for example precipitates and solutions (especially titration end-points). Please include with the scripts a note of the index numbers of such candidates. Experience suggests that candidates who are red/green colour-blind – the most common form – do not generally have significant difficulty. Reporting such cases with the scripts removes the need for a ‘Special Consideration’ application for this handicap.

Accuracy of Solutions

1 All the solutions are to be labelled as shown and they should be bulked and mixed thoroughly before use to ensure uniformity.

2 Every effort should be made to keep the concentrations accurate to within one part in two hundred of those specified.

3 If the concentrations differ slightly from those specified, the Examiners will make the necessary allowance. They should be informed of the exact concentrations.

4 It should also be noted that descriptions of solutions given in the question paper may not correspond exactly with the specification in these Instructions. The candidates must assume the descriptions given in the question paper.

5 In view of the difficulty of the preparation of large quantities of solution of uniform concentration, it is recommended that the maximum number of candidates per group be 30 and that separate supplies of solutions be prepared for each group.

6

UCLES 2006 9701/31/SP07

Responsibilities of the Supervisor

(i) The Supervisor, or other competent chemist must carry out the experiments in question 1 and complete the table of readings on a spare copy of the question paper which should be labelled ‘Supervisor’s Results’.

This should be done for: each session held and each laboratory used in that session, and each set of solutions supplied.

N.B. The question paper cover requests the candidate to fill in details of the examination session and the laboratory used for the examination.

It is essential that each packet of scripts contains a copy of the applicable Supervisor’s Results as the candidates’ work cannot be assessed accurately without such information.

(ii) The Supervisor must complete the Report Form on page 7 to show which candidates attended each session. If all candidates took the examination in one session, please indicate this on the Report Form. A copy of the Report Form must accompany each copy of the Supervisor’s Results in order for the candidates’ work to be assessed accurately.

(iii) The Supervisor must give details on page 8 of any particular difficulties experienced by a candidate, especially if the Examiner would be unable to discover this from the written answers.

Each envelope returned to Cambridge must contain the following items.

1 The scripts of those candidates specified on the bar code label provided.

2 A copy of the Supervisor’s Report relevant to the candidates in 1.

3 A copy of the Report Form, including details of any difficulties experienced by candidates (see pages 7 and 8).

4 The Attendance Register.

5 A Seating Plan for each session/laboratory.

Failure to provide appropriate documentation in each envelope may cause candidates to be penalised.

7


9701/3

REPORT FORM

This form must be completed and sent to the Examiner in the envelope with the scripts.

Centre Number ………………………………… Name of Centre ………………………………………

1 Supervisor’s Results

Please submit details of the readings obtained in Question 1 on a spare copy of the question paper clearly marked ‘Supervisor’s Results’ and showing the Centre number and appropriate session/laboratory number.

2 The index numbers of candidates attending each session were:

First Session Second Session

3 The Supervisor is required to give details overleaf of any difficulties experienced by particular candidates, giving names and index numbers. These should include reference to:

(a) any general difficulties encountered in making preparation;

(b) difficulties due to faulty apparatus or materials;

(c) accidents with apparatus or materials;

(d) assistance with respect to colour-blindness.

Other cases of hardship, e.g. illness, temporary disability, should be reported direct to CIE on the normal ‘Application for Special Consideration’ form.

4 A plan of work benches, giving details by index numbers of the places occupied by the candidates for each experiment for each session, must be enclosed with the scripts.

�

8

UCLES 2006 9701/31/SP07

Report on any difficulties experienced by candidates.





CHEMISTRY 9701/04

Paper 4 Structured Questions


SPECIMEN PAPER

. 1 hour 45 minutes

Candidates answer on the Question Paper. Additional Materials: Data Booklet


Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B

Answer all questions. You may lose marks if you do not show your workings or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

This document consists of 17 printed pages and 1 blank page.



2

SP/QP/9701/04

For

Examiner's

Use Section A Answer all the questions in the spaces provided.

1 Bromine can react with methanoic acid according to the following equation. Br2(aq) + HCO2H(aq) → 2Br-(aq) + 2H+(aq) + CO2(g) (a) (i) What maximum volume of gas, measured at r.t.p., would be produced by reacting

3.2 g of bromine? (ii) Suggest how the rate of the reaction might be followed.

[5] (b) The graph opposite contains information about this reaction. (i) What evidence is there to suggest that this reaction is first order with respect to

bromine?

(ii) Write a simple equation relating the rate of reaction to the concentration of bromine

under these conditions.

(iii) Calculate the half-life of this reaction.

[5]

[Total : 10]

3


For

Examiner's

Use

4

UCLES 2006 9701/04/SP07

For

Examiner's

Use 2 (a) Define the standard enthalpy change of formation of a compound.

[2] The standard enthalpy change of formation of SiCl4(g) is –610 kJ mol-1. The standard enthalpy changes of atomisation of the elements silicon and chlorine are

+338 and +122 kJ mol-1 of atoms respectively.

(b) Use these values to construct an energy cycle to show the formation of SiCl4(g). [2] (c) (i) Hence calculate the average bond energy of the Si-Cl bond from these data.

(ii) Suggest why the calculated value is different from the value given in the Data Booklet.

[2]

5


For

Examiner's

Use

(d) Pure silicon is made by reducing SiCl3H with hydrogen at a high temperature.

(i) Construct a balanced equation for this reaction.

(ii) The bond energy of the Si-Br bond is 298 kJ mol-1. Use this value, and other bond energy values given in the Data Booklet to suggest whether the reaction between SiBr3H and hydrogen would be more or less endothermic than the reaction between SiCl3H and hydrogen.

(iii) State a use of pure silicon.

[4] [Total : 10]

6

UCLES 2006 9701/04/SP07

For

Examiner's

Use 3 Agricultural lime is manufactured from limestone (calcium carbonate) by first heating the rock to a high temperature in a lime kiln. The product is allowed to cool and a calculated amount of water is added. A highly exothermic reaction takes place and a white powder called ‘slaked lime’ is produced.

(a) Write balanced equations for these two reactions.

[2] (b) Give two reasons why lime is used in agriculture.

[2]

(c) How does the temperature required to decompose the carbonates of Group II elements vary down the group, and why is this so?

[3]

(d) The mineral dolomite is a double carbonate of magnesium and calcium, with the formula CaMg(CO3)2. When 1.000 g of an impure sample of dolomite was completely dissolved in an excess of hydrochloric acid, 0.450 g of carbon dioxide was given off.

(i) Write a balanced equation for the reaction.

(ii) Calculate the percentage purity of the dolomite. [3] [Total : 10]

7


For

Examiner's

Use

4 (a) State the electronic configurations of

(i) the Cu atom,

(ii) the Cu+ ion,

(iii) the Cu2+ ion.

[2] (b) Explain the origin of colour in transition metal compounds, and use your explanation to

suggest why copper(I) chloride is white, whereas copper(II) chloride is blue.

[4] (c) (i) Write equations to show the reactions that occur when dilute ammonia solution is

slowly added to a solution of CuCl2 until the ammonia is in excess.

(ii) What type of chemical reaction is occurring? Explain your answer.

[4] [Total: 10]

8

UCLES 2006 9701/04/SP07

For

Examiner's

Use 5 The elements in Group VII show trends in a number of their physical and chemical properties.

(a) Explain the trend in boiling points of the elements as shown.

element boiling point/oC

chlorine -35

bromine +59

iodine +184

[2] (b) There are also clear trends in both the H-X bond energy and the Eθ values for the cell

½X2(aq)/X -(aq), where X = Cl, Br, I. Use relevant data from the Data Booklet to describe and explain each of the following.

Give an equation for each reaction that occurs. (i) The reactions of the halide ions with concentrated sulphuric acid.

9


For

Examiner's

Use

(ii) The action of heat on the hydrogen halides.

[8] [Total : 10]

10

UCLES 2006 9701/04/SP07

For

Examiner's

Use 6 An organic compound, A, has the composition by mass C, 40.0%; H, 6.65%; O, 53.3%.

(a) Show that the empirical formula of A is CH2O. [1]

(b) A shows the following properties or reactions. State what can be deduced about A from each of these.

(i) It is optically active.

(ii) It gives a brisk effervescence with aqueous sodium carbonate.

(iii) It gives a yellow precipitate when warmed with alkaline aqueous iodine.

[3]

(c) Suggest an identity for A and draw its displayed formula. [1]

(d) Give the displayed formula of the organic product formed when A is warmed with acidified potassium dichromate(VI).

[1]

11


For

Examiner's

Use

(e) When A is warmed with concentrated sulphuric acid, a cyclic compound of molecular

formula C6H8O4 can be isolated. Suggest a displayed formula for this cyclic compound, and state what functional group

is present in the molecule. [2]

(f) A has a non optically active isomer, B. Under the reaction conditions described in (e), compound B produces compound C, C3H4O2. Suggest a structure for C.

[2] [Total : 10]

12

UCLES 2006 9701/04/SP07

For

Examiner's

Use 7 Aspartame is a synthetic sweetening agent that is 180 times as sweet as sugar.

H2N — CH — CO — NH — CH — CO2 — CH3

│ │ CH2 CH2 │ │ CO2H C6H5

aspartame (a) (i) Name four different functional groups in the aspartame molecule.

1 2

3 4

(ii) Identify two functional groups in aspartame which contribute to its solubility in water. Give a reason for your answer.

1 2

Reason

[4] (b) (i) Suggest conditions and reagents that could be used to hydrolyse aspartame into

its constituent parts.

(ii) Draw the structural formulae of all of the organic molecules obtained by hydrolysing aspartame.

[5]

(c) Suggest why aspartame is not used as a sweetening agent in baked products.

[1] [Total : 10]

13


For

Examiner's

Use

Section B – Applications of Chemistry

Answer all the question in the spaces provided. 8 (a) Explain how protein synthesis occurs in cells, including in your answer the role of

ribosomes.

[6]

(b) Explain why the enzyme lysozyme, which consists of 129 amino acid residues, requires

a triplet code of 393 bases.

[2]

(c) (i) Name a disease brought about by a mutation in the DNA of the individual.

(ii) Give a symptom of the disease.

[2] [Total : 10]

14

UCLES 2006 9701/04/SP07

For

Examiner's

Use 9 (a) An aromatic compound D, of Mr 122, is a possible sex attractant for insects. It has the

following composition by mass: C, 78.7%; H, 8.2%; O, 13.1%. What is the molecular formula of D? [3]

(b) The NMR spectrum of D is shown below.

Identify the parts of the molecule responsible for each group of peaks. Use your

answer to deduce a structure for D, explaining your reasoning.

[5]

15


For

Examiner's

Use

(c) Explain what effect you would expect the addition of a small amount of D2O to have on

the NMR spectrum of D.

[2]

(d) An isomer of D shows no effect on the NMR spectrum on adding D2O. Draw the structure of the isomer and suggest how its NMR spectrum would differ from

that of D.

[3]

[Total : 13]

16

UCLES 2006 9701/04/SP07

For

Examiner's

Use 10 Read the passage about the production of ethanol for fuel, and then answer the questions. Sugar cane is the world’s largest source of fermentation ethanol. Ethanol can be produced

by converting the starch content of biomass feedstocks, such as sugar cane, into alcohol. Yeast is used to break down the complex sugars of starch into simpler sugars, which are fermented to form ethanol. A further advantage is that bagasse, the remains of the cane after the sugar is extracted, and the tops and leaves of the sugar cane can be used as a fuel for electricity production. An efficient ethanol distillery using sugar cane by-products can therefore be self-sufficient and also generate a surplus of electricity.

There is a second process that utilises biomass feedstocks to produce ethanol. The main

carbohydrate constituent of these feedstocks is cellulose, which, like starch, is a sugar polymer that can be broken down by hydrolysis into simpler sugars. The new process uses enzymatic hydrolysis or acid hydrolysis of cellulose to produce simple sugars for fermentation.

The use of bagasse as the cellulose source in the new process could allow off-season

production of ethanol with very little new equipment. This process is relatively new and is not yet commercially available, but potentially can use a much wider variety of abundant, inexpensive feedstocks. Alcohol fuels have been developed in a number of African countries – Kenya, Malawi, South Africa and Zimbabwe – currently producing sugar, with others, including Mauritius, Swaziland and Zambia also having great potential.

Ethanol has different chemical properties from gasoline. Although one litre of ethanol has

about two-thirds of the energy of a litre of gasoline, tuning the engine for ethanol can make up as much as half the difference. Furthermore, should there be a spill, ethanol can be dealt with more quickly and easily than gasoline.

Using ethanol even in low-level blends (e.g. E10 – which is 10% ethanol, 90% gasoline) can have environmental benefits. Tests show that E10 produces less carbon monoxide, sulphur dioxide and carbon dioxide than gasoline. Higher blends (E85 – 15% gasoline), or even neat ethanol burn with less of almost all these pollutants.

(a) Explain two ways in which bagasse can be used to reduce the cost of ethanol

production.

(i)

(ii)

[2]

17

© UCLES 2006 9701/4/SP07

For

Examiner's

Use

(b) In addition to ethanol, what other product is formed in the fermentation of sugars by yeast?

[1]

(c) Suggest an equation to show the hydrolysis of cellulose in bagasse to form fermentable

sugars with the molecular formula C6H12O6. [1]

(d) Using your knowledge of chemical bonding, suggest why a spill of ethanol is more easily dealt with than a spill of gasoline.

[3]

[Total : 7]

18

UCLES 2006 9701/04/SP07

BLANK PAGE


Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.


Specimen for 2007

GCE A LEVEL

MARK SCHEME

MAXIMUM MARK: 100

SYLLABUS/COMPONENT: 9701/04

CHEMISTRY

PRACTICAL


Mark Scheme Syllabus Paper

GCE A LEVEL – 2007 9701 4

© University of Cambridge International Examinations 2006

Section A

1 (a) (i) 2 x 80g of Br2 produce 24 dm3 of CO2 (1)

Thus 3.2 g of Br2 will produce 802

242.3

x

x = 0.48 dm3 (1)

(ii) Colorimetrically : withdraw samples periodically (1) measure absorbance (1) plot absorbance against time (1) OR Iodometrically : oxidising I- to I2 (1) by Br2 (1) titrating with thiosulphate (1)

(Allow titration of H+ or evolution of CO2 if some mention of solubility.) [5]

(b) (i) Reaction has a constant half-life (1) evidence from graph that t(1/2) is constant (1)

(ii) Rate = [Br2] (1)

(iii) At least two measurements of half-life from first graph (1) Calculation of mean (say 200 secs) (1) [5]

Total :10

2 (a) The standard enthalpy change of formation of a compound is the enthalpy change when one mole of a compound is formed (under standard conditions) (1) from its elements in their standard states. (1) [2]

(b) Suitable cycle clearly labelled showing all three values [2]

(c) (i) 298 kJ mol-1 (1)

(ii) In Data Booklet Si-Cl bond energy is 210 kJ mol-1. SiCl4 is not a gas under standard conditions (1) [2]

(d) (i) SiCl3H + H2 → Si + 3HCl (1)

(ii) From the Data Booklet, ESi-Cl = 359, EH-Cl = 431, EH-Br = 366 kJ mol-1

Per Si-hal bond, for SiCl3H, ∆H= 359 - 431 = -72, for SiBr3H, ∆H = 298 - 366 = -68 (1) therefore the reaction with SiBr3H will be less exothermic i.e. overall reaction would be more endothermic (1)

OR ∆Hreaction: for SiCl3H, ∆Hreaction = + 96, and for SiBr3H, ∆Hreaction = +108 (1) therefore overall reaction is more endothermic (1)

(iii) Manufacture of semiconductors (or equivalent) (1) [4] Total : 10


GCE A LEVEL – 2007 9701 4


3 (a) CaCO3 → CaO + CO2 (1)

CaO + H2O → Ca(OH)2 (1) [2] (b) To neutralise acid soils (1) To improve soil ‘quality’ by precipitating clays (or equivalent) (1) [2] (c) The temperature increases (1) As the Group is descended, the cation increases in size (1) Thus ability of the cation to polarise the anion decreases, increasing the stability of the carbonate. (1) [3]

(d) (i) CaMg(CO3)2 + 4HCl → CaCl2 + MgCl2 + 2CO2 + 2H2O (1) (ii) Mr of dolomite is 40 + 24 + (2 x 60) = 184 (1) 184 g of dolomite should produce 2 x 44 g of CO2

Hence 1 g of dolomite should give 184

88g of CO2 = 0.478 g

% purity of the dolomite is 478.0

100450.0 x = 94.1% (1)

[3] Total : 10 4 (a) (i) [Ar] 3d10 4s1

(ii) [Ar] 3d10

(iii) [Ar] 3d9 [2] (b) Any four of the following points:

• colour due to absorption of certain visible frequencies

• d-orbitals are split into two groups by presence of ligands

• light absorbed when e- moves from lower to higher orbital

• this needs a gap in the higher orbital, so d10 in Cu(I) is not coloured

• if CuCl2 is blue, then photons absorbed must be red ones [4]

(c) (i) [Cu(H2O)6]2+ + 2OH- → [Cu(H2O)4(OH)2] + 2H2O

(NH3 + H2O → NH4

+ + OH-)

[Cu(H2O)4(OH)2] + 4NH3 → [Cu(NH3)4]2+ + 2OH- + 4H2O

(or → [Cu(NH3)4(H2O)2 ]2+ ) (2)

(ii) These are ligand exchange reactions. H2O is exchanged for OH-, and H2O and OH- are exchanged for NH3. (2) [4] [Total : 10]


GCE A LEVEL – 2007 9701 4


5 (a) Van der Waals forces increase with the number of electrons present (1) Since this allows larger dipoles and hence stronger attractive forces (1) [2] (b) (i) Description of Cl

-, Br-, and I- with conc sulphuric acid 3 x (1) Use of Eo (1) (ii) Description of HCl, HBr and HI 3 x (1) Use of Eo (1) [8] Total : 10 6 (a)

element % Ar % / Ar ratio

C 40.0 12 3.33 1

H 6.65 1 6.65 2

O 53.3 16 3.33 1

[1] (b) (i) It contains an asymmetric carbon atom (1) (ii) It contains a carboxylic acid group (1) (iii) It contains a CH3CH(OH)- or CH3CO- group (1) [3] (c) Displayed formula of 2-hydroxypropanoic acid [1] (d) Displayed formula of the ketone of the above [1] (e) Displayed formula of the cyclic di-ester (1) Ester (1) [2] (f) Displayed formula of 3-hydroxypropanoic acid (1) Compound C is CH=CHCO2H (1) [2] Total : 10


GCE A LEVEL – 2007 9701 4


7 (a) (i) 1. amine 2. carboxylic acid 3. amide 4. ester (2) (ii) 1. amine 2. carboxylic acid (1) Both can form ions (both polar groups) by gain or loss of a

proton from water or form hydrogen bonds with water (1) [4] (b) (i) Allow conc. HCl and heat or conc. NaOH and heat 2 x (1) (ii) Diagrams of aspartic acid, phenylalanine and methanol 3 x (1) [5] (c) It could be decomposed/hydrolysed during cooking [1] Total :10

Section B 8 (a) 6 points from the following :

• 2 strands of DNA separate

• mRNA reads the ‘code’/base sequence on the DNA

• mRNA moves out of the nucleus

• mRNA binds to the ribosome

• tRNA binds to amino acids

• amino acids are transferred to ribosome and joined to growing chain

• until Stop codon is reached [6] (b) Each amino acid needs 3 bases to code for it (1) 3 x 129 = 387, which leaves 3 bases to code for Start and 3 for Stop (1) [2] (c) (i) A variety of answers possible e.g.

• sickle cell disease

• thallassemia

• cystic fibrosis

• haemophilia etc. (1) (ii) A suitable symptom e.g.

• Deformed red blood cells

• Restricts production of haemoglobin

• Mucous lining of lungs thickens

• Poor clotting of blood/bleeding under the skin (1) [2]

Total : 10


GCE A LEVEL – 2007 9701 4


9 (a) % %/Ar Ratio C 78.7 6.56 8 ) Empirical formula H 8.2 8.2 10 ) (1) C8 H10O (1) O 13.1 0.82 1 ) Mr = 122, hence this molecular formula Molecular formula is C8H10O (1) [3]

(b) 1.2δ - CH3 (1)

2.5δ - CH2 (1)

5.5δ - OH (1)

6.8δ aryl hydrogens x 4 (1) Hence structure is CH3CH2- -OH (1) (or ethyl phenol isomers) [5]

(c) Peak at 5.5δ would disappear (1) Due to rapid exchange with D+ which does not absorb here (1) [2] (d) CH3OCH2 - or isomers (1) Two sensible suggestions (2) [3]

Total : 12 10 (a) Can be used as a fuel (for generating electricity) (1) Can be hydrolysed (using acid or enzymes) and the sugars fermented (1) [2]

(b) Carbon dioxide [1]

(c) (C6H10O5)n + nH2O → nC6H12O6 [1] (d) Ethanol has an –OH group and so can be washed away Gasoline is a hydrocarbon and is not soluble in water Gasoline requires detergent which can add to the pollution Ethanol is biodegradable (any 3) [3]

Total : 7





CHEMISTRY 9701/05

Paper 5 Planning, analysis and evaluation


SPECIMEN PAPER 1 hour 15 minutes Candidates answer on the Question Paper. .


Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. You are advised to show all working in calculations. Use of Data Booklet is unnecessary. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question.

For Examiner’s Use

1

2

TOTAL

This document consists of 9 printed pages and 1 blank page.



2

UCLES 2006 9701/05/SP07

For

Examiner's

Use

1 Hydrochloric acid reacts with solid calcium carbonate in the form of marble chips. The

products of the reaction are aqueous calcium chloride, carbon dioxide gas and water.

2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(l) You are to plan an investigation to find how changes in one variable affect the rate of

reaction. (a) (i) The concentration of the hydrochloric acid is one independent variable that could

be investigated. Identify two other independent variables that could be investigated.

[2]

(ii) Identify a dependent variable that you could measure to follow the rate of reaction.

[1]

(b) Propose a hypothesis that can be tested experimentally and that links the rate of

reaction and the concentration of the hydrochloric acid.

[1]

(c) Design a laboratory experiment that you would use to investigate your hypothesis. You

should draw a labelled diagram showing the arrangement of your apparatus. Your plan should include the following.

(i) a step-by-step description of the procedure you would follow (ii) how you would measure the independent variable (iii) how you would vary the independent variable and how you will ensure accuracy in

your results (iv) how you would control the other two variables that you identified in part (a) (v) any safety precautions that you would take (vi) appropriate quantities (masses, volumes, concentrations) to use in the experiment [Ar: Ca, 40.1; C, 12.0; O, 16.0] Concentrated hydrochloric acid, a corrosive liquid, has an approximate

concentration of 11 mol dm-3.

3


For

Examiner's

Use Labelled diagram

Plan

[8]

4

UCLES 2006 9701/05/SP07

For

Examiner's

Use

(d) Prepare a table showing all of the data you wish to record in the experiment and any

columns for processing the data recorded. Explain how you will use the data to confirm or reject the hypothesis proposed in (b).

[3]

[Total : 15]

5


For

Examiner's

Use

2 A student makes the following prediction. “The amount of carbon dioxide evolved when a metal carbonate, X2CO3, reacts with an

excess of an acid is directly proportional to the moles/mass of the carbonate used.” If this statement is true the relative molecular mass of X2CO3 can be determined by the

following simple experiment.

• The mass of a weighing bottle + X2CO3 is measured.

• 50 cm3 of 2.0 mol dm-3 hydrochloric acid (an excess) is transferred from a measuring cylinder to a 250 cm3 conical flask.

• Sodium carbonate is added to the acid in the flask to saturate the acid with carbon dioxide so that none of the gas given off when X2CO3 reacts with the acid will dissolve in the acid.

• A cotton wool plug is placed in the neck of the flask and the flask + acid is weighed.

• The weighed X2CO3 is added to the acid in the flask and the cotton wool plug quickly replaced in the neck of the flask to prevent any loss of acid spray.

• The empty weighing bottle is weighed.

• When reaction in the flask has stopped, the flask is left for 10 minutes to allow carbon dioxide to diffuse from the flask.

• The flask and its contents after the reaction are weighed. The results from a group of students are given in the table overleaf.

6

UCLES 2006 9701/05/SP07

For

Examiner's

Use

A B C D E F G H

mass of weighing bottle + X2CO3

/g

mass of empty weighing bottle

/g

mass of flask + acid before the reaction

/g

mass of flask + solution after the reaction

/g

14.29 11.48 221.35 223.21

16.41 11.76 209.71 212.91

12.24 11.34 210.45 210.97

16.77 11.27 214.38 217.80

16.48 10.68 211.63 215.59

14.85 11.15 217.18 219.68

13.81 11.61 212.12 213.76

18.81 11.06 218.65 224.25

16.18 10.94 206.77 210.31

17.93 11.53 221.49 225.84

14.49 11.09 217.18 219.68

18.19 10.87 215.33 220.31

(a) Use the additional columns of the table to record calculated values that will enable you

to determine Mr for X2CO3 graphically. You may use some or all of the columns. Label the columns you use, including the units and an equation to show how the value is calculated. You may use the column headings A to H in these equations e.g. = C - B. (Remember that the gas is lost from the flask after the weighed carbonate is added to the weighed acid.)

[2]

7


For

Examiner's

Use (b) Present the data calculated in (a) in graphical form. Draw the line of best-fit. [4]

8

UCLES 2006 9701/05/SP07

For

Examiner's

Use

(c) Circle any anomalous points on the graph that you did not use when drawing the best-fit

line. By reference to the description of the experiment, suggest an explanation for any anomaly.

[2]

(d) Identify any part of the range of readings where the data appears to be less reliable

and suggest why this should be the case.

[1]

(e) Use data obtained from the best-fit line you have drawn to calculate Mr for X2CO3.

X2CO3(s) + 2H+(aq) → 2X+(aq) + CO2(g) + H2O(l)

The Mr of X2CO3 is

[2]

9

© UCLES 2006 9701/05/SP07

For

Examiner's

Use (f) By considering the data you have processed and the graph you have drawn, explain

whether the experimental data supports the initial prediction and whether the experimental procedure described is suitable for the determination of Mr.

[2]

(g) Suggest an improvement to the experimental procedure that has been described.

[1]

(h) Use your knowledge of acid-base chemistry to describe a more appropriate way by

which the Mr of a metal carbonate might be determined.

[1]

[Total : 15]

10

UCLES 2006 9701/05/SP07

BLANK PAGE


Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity.

University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

sp 2007(3-5)

Documents