Paper 4

Centre Number

Candidate Number

Candidate Name

UNIVERSITY OF CAMBRIDGE LOCAL EXAMINATIONS SYNDICATE Joint Examination for the School Certificate and General Certificate of Education Ordinary Level

5070/4

CHEMISTRY PAPER 4 Alternative to Practical Wednesday

27 OCTOBER 1999

1 hour

Candidates answer on the question paper. Additional materials: Electronic calculator and/or mathematical tables

TIME

1 hour

INSTRUCTIONS TO CANDIDATES Write your name, Centre number and candidate number in the spaces at the top of this page. Answer all questions. Write your answers in the spaces provided on the question paper. All essential working must be shown. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You should use names, not symbols, when describing all reacting chemicals and the products formed. Mathematical tables are available. You may use a calculator.

FOR EXAMINER’S USE

This question paper consists of 19 printed pages and 1 blank page. SB (SM) QK94136/3 © UCLES 1999

[Turn over

2 1

Name the piece of apparatus shown.

Answer ...............................................................................................................................[1]

2

A student added 100 cm3 of 1.00 mol / dm3 barium nitrate to 100 cm3 of 2.00 mol / dm3 sodium sulphate. Barium sulphate was produced. (a) (i)

Give the formula of barium sulphate. ..................................................................................................................................

(ii)

Describe the appearance of barium sulphate in the resulting mixture. ..................................................................................................................................

(iii)

How could the barium sulphate be removed from the mixture? .................................................................................................................................. [3]

(b) Which of the reagents, barium nitrate or sodium sulphate, was in excess? Explain your answer. answer ............................................................................................................................ explanation ..................................................................................................................... ......................................................................................................................................... [2]

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3 (C) (i)

The student expected a yield of 0.100 mol of barium sulphate. Calculate the expected mass of barium sulphate, using your answer in (a) (i).

For Examiner’s Use

[A r: Ba = 56, S = 32, O = 16]

.............................................................................................................................. g (ii)

The mass of dry barium sulphate was 12.5 g. Calculate the percentage yield of barium sulphate.

.................................................................................................................................. [2]

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4 3

A student used the apparatus shown to produce ethanoic acid, CH3COOH.

water out

B

water in

an alcohol + an oxidising agent heat A small volume of an alcohol was placed in the flask together with an oxidising agent. The mixture was warmed and a colour change was seen in the flask. (a) (i)

Name and give the formula of the alcohol. name ....................................................................................................................... formula ....................................................................................................................

(ii)

Suggest a suitable oxidising agent. ..................................................................................................................................

(iii)

What colour change was seen using the oxidising agent stated in (a) (ii)? .................................................................................................................................. [4]

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5

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(b) Name the piece of apparatus marked B on the diagram. What is its purpose? name .............................................................................................................................. purpose .......................................................................................................................... ......................................................................................................................................... [2] (c) Suggest two items which the student should wear to ensure personal safety, when carrying out the experiment. 1.

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

2.

.................................................................................................................................. [2]

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6

For Examiner’s Use

In questions 4 – 8 inclusive place a tick ✓ in the box against the best answer. 4

A student made a sample of the ester methyl propanoate, C2H5COOCH3. Which two compounds were heated together? (a) ethanoic acid and methanol (b) ethanoic acid and ethanol (c) propanoic acid and methanol (d) propanoic acid and ethanol

5

[1]

A student did two experiments to produce carbon dioxide. Experiment 1.

5.0 g of marble and 10 cm3 of 1.0 mol / dm3 hydrochloric acid.

Experiment 2.

5.0 g of marble and 20 cm3 of 1.0 mol / dm3 hydrochloric acid.

The temperature of the acid was the same at the start of each experiment. Graphs were drawn of the volume of carbon dioxide against time. Which two graphs best represent the two experiments?

volume of CO2 /cm3

volume of CO2 /cm3

volume of CO2 /cm3

time/min

time/min

time/min

(A)

(B)

(C)

experiment 1

experiment 2

(a)

A

B

(b)

A

C

(c)

B

C

(d)

B

A [1] 5070/4 W99

7 6

For Examiner’s Use

A student added powdered zinc to aqueous copper(II) sulphate in a beaker. Which of the following observations was incorrect? (a) the zinc dissolved (b) the colour of the solution changed to blue (c) a brown deposit was seen

7

[1]

The following chromatogram was obtained in an experiment to compare two dyes, dye 1 and dye 2.

solvent front

start line Dye 1

Dye 2

blue

yellow

red

Which statement is correct? (a) only one dye contains red (b) only one dye contains yellow (c) both dyes contain blue (d) both dyes contain all three colours

[1]

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8 8

For Examiner’s Use

A student did some tests on substance X. 1.

X has a high melting point.

2.

Solid X does not conduct electricity.

What could substance X have been? (a) ethanol (b) graphite (c) sodium chloride (d) sugar

9

[1]

Washing soda is the common name for hydrated sodium carbonate, Na2CO3.x H2O. A student determined the value of x in the formula by titration with 0.100 mol / dm3 hydrochloric acid (solution S). A sample of Na2CO3.x H2O was added to a previously weighed container which was then reweighed. Mass of container + Na2CO3.x H2O

=

8.34 g

Mass of container

=

4.79 g

(a) Calculate the mass of Na2CO3.x H2O

............................................................................................................................. g

[1]

The sample of Na2CO3.x H2O was placed in a flask and made into 250 cm3 of solution with distilled water. This was solution T. 25.0 cm3 of T was transferred into a flask. (b) Which piece of apparatus is most suitable for transferring 25.0 cm3 of T?

.....................................................................................................................................[1] Two drops of methyl orange indicator were added to T. Solution S was run in from a burette until the end point was reached. (c) What was the colour change at the end point? The colour changed from ............................................................................................... to ......................................................................................................... at the end point. [1] 5070/4 W99

9 (d) Three titrations were done. The diagrams below show parts of the burette with the liquid levels before and after each titration. first titration

second titration

For Examiner’s Use

third titration

28

0 25

3 11 36

29 1 4

26

12 37

Use the diagrams to complete the following results table. first

titration

second

third

final reading / cm3 initial reading / cm3 volume of S best titration results (✓) Summary. Tick (✓) the best titration results. Using these results, the average volume of S was ......................................................... cm3.

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[4]

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10 (e) Calculate the number of moles of hydrochloric acid in the average volume calculated in (d).

.................................................................. moles (f)

[1]

Sodium carbonate reacts with hydrochloric acid according to the following equation. Na2CO3 + 2HCl

2NaCl + CO2 + H2O

Calculate the number of moles of sodium carbonate which reacts with the number of moles of hydrochloric acid calculated in (e).

.................................................................. moles

[1]

(g) Calculate the number of moles of sodium carbonate in 250 cm3 of solution T.

.................................................................. moles

[1]

(h) Calculate the relative molecular mass of sodium carbonate Na2CO3. [Ar: Na, 23; C, 12; O, 16.]

.................................................................. (i)

[1]

Using your answers to (g) and (h), calculate the mass of sodium carbonate, Na2CO3, in the 250 cm3 of solution T.

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

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[1]

For Examiner’s Use

11 (j)

By subtracting your answer in (i) from answer (a), calculate the mass of water in the original sample of hydrated sodium carbonate.

.................................................................. g

For Examiner’s Use

[1]

(k) Using your answers (i) and (j) in the following formula, calculate the value of x in Na2CO3.x H2O. x =

106 x answer (j) 18 x answer (i)

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

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[1]

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12 10 The following table shows the tests a student did on substance M and the conclusions made from the observations. Complete the table by describing these observations and suggest the test and observations which led to the conclusion from test 4.

test

observations

conclusion

1

M was dissolved in water and the solution divided into three parts for tests 2, 3 and 4.

M is a compound of a transition metal.

2

(a) To the first part, aqueous sodium hydroxide was added until a change was seen.

M may contain Cu2+ ions.

(b) An excess of aqueous sodium hydroxide was added to the mixture from (a).

3

The presence of Cu2+ ions is confirmed.

(a) To the second part, aqueous ammonia was added until a change was seen. (b) An excess of aqueous ammonia was added to the mixture from (a).

M contains NO3– ions.

4

Conclusion: The formula for substance M is ............................................................. .

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[9]

For Examiner’s Use

13 11 A student found the solubility, in water, of potassium nitrate, using the apparatus shown.

For Examiner’s Use

thermometer

solution

crystals of the salt

heat 10.0 g of water was put into a boiling tube. To this, 3.0 g of potassium nitrate were added. The tube and contents were heated until the solid dissolved. The tube was allowed to cool. At the first sign of solid appearing, the temperature was taken. The experiment was repeated using 5.0, 7.0 and 9.0 g of potassium nitrate.

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14 (a) The thermometer stems below show the temperatures at which the solid appeared. Use these values to complete the table.

50

80

90

100

40

70

80

90

30

60

70

80

20

50

60

70

10

40

50

60

0

30

40

50

3.0 g potassium nitrate

5.0 g potassium nitrate

Mass of potassium nitrate in 10.0 g of water / g

7.0 g potassium nitrate

3.0

5.0

9.0 g potassium nitrate

7.0

9.0

Temperature at which solid appeared / °C [2]

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15 The graph shows the results obtained in a similar experiment to find the solubility of sodium nitrate.

For Examiner’s Use

(b) Plot the results for potassium nitrate on the same axes and join the points with a smooth curve.

12 mass, in grams, of salt in 10 g of water 10

8 sodium nitrate 6

4

2

0 0

20

40

60

80 100 temperature/ °C [2]

Use the graphs to answer the following questions. (c) (i)

At what temperature were the dissolved masses equal?

............................................................................. °C (ii)

What was the mass of the dissolved salts at this temperature?

............................................................................. g 5070/4 W99

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16 (d) What mass of potassium nitrate will crystallise when the saturated solution at 80 °C is cooled to 30 °C? Mass of potassium nitrate dissolved at 80 °C =

......... g

Mass of potassium nitrate dissolved at 30 °C =

......... g

Mass of potassium nitrate that crystallises on cooling from 80 °C to 30 °C

......... g

=

[2] (e) The solubility of a salt is defined as the maximum mass which will dissolve in 100 g of water at a given temperature. Calculate the solubility of potassium nitrate at 50 °C.

.................................................................................... g

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[1]

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17

For Examiner’s Use

12 This question concerns water. (a) (i)

Name a gas that may be used to sterilise water.

.................................................................................................................................. (ii)

Give a test for this gas.

.................................................................................................................................. [2] (b) What is used to measure the pH of a sample of water?

.....................................................................................................................................[1]

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18 (c) The apparatus shown was used for the electrolysis of water. S

T

carbon electrodes

water containing a little sulphuric acid

+

–

battery (i)

Why was a little sulphuric acid added to the water?

.................................................................................................................................. (ii)

Name the gas produced in tube S.

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

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19 (iii)

Name the gas produced in tube T.

.................................................................................................................................. (iv)

Compare the volume of gas produced in S with the volume produced in T.

.................................................................................................................................. [4]

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20 BLANK PAGE

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