June 2000 - Paper 4

Centre Number

Candidate Number

Candidate Name

UNIVERSITY OF CAMBRIDGE LOCAL EXAMINATIONS SYNDICATE General Certificate of Education Ordinary Level

CHEMISTRY

5070/4

PAPER 4 Alternative to Practical MAY/JUNE SESSION 2000

1 hour

Candidates answer on the question paper. Additional materials: Mathematical tables Ruler (cm/mm)

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. 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 13 printed pages and 3 blank pages. SB (SLC/DJ) QF06371/4 © UCLES 2000

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For Examiner’s Use

2 1

(a) Name the apparatus shown below.

......................................................................................................................................[1] (b) (i)

What safety item should be used with this apparatus? ...................................................................................................................................

(ii)

Why is this safety item used? ...............................................................................................................................[2]

2

A student did two experiments as shown below.

air

glass disc

bromine vapour cold water bromine liquid

crystal of copper(II) sulphate diagram 1

diagram 2

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3 (a) A student was given a crystal of copper(II) sulphate. He placed the crystal in a beaker of cold water as shown in diagram 1. (i)

For Examiner’s Use

What is the colour of copper(II) sulphate crystals? ...................................................................................................................................

What changes were seen in the appearance of the contents of the beaker. (ii)

after a few minutes, ................................................................................................................................... ...................................................................................................................................

(iii)

after several hours? ................................................................................................................................... ................................................................................................................................... [3]

(b) The student set up the apparatus as shown in diagram 2. Then he carefully removed the glass disc allowing the contents of the gas jars to mix. What change was seen after a few minutes? .......................................................................................................................................... ......................................................................................................................................[1] (c) (i)

Name the process that was illustrated by both of the experiments. ...................................................................................................................................

(ii)

Explain why the changes observed in (a) took place. ................................................................................................................................... ...................................................................................................................................

(iii)

Explain why the change observed in (b) was faster than the change in (a). ................................................................................................................................... ................................................................................................................................... [3]

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For Examiner’s Use

4 3

+

–

+

–

A

B

C

D

aqueous sodium chloride

molten sodium chloride heat

The diagram shows two electrolytic cells. Each of the electrodes is labelled with a letter. Use these letters to answer the questions below. (a) At which electrode was a metal produced? ......................................................................................................................................[1] (b) (i)

At which two electrodes was the same gas evolved? electrodes ........... and ........... .

(ii)

Name this gas. ...................................................................................................................................

(iii)

Give a test for this gas. ................................................................................................................................... ................................................................................................................................... [3]

(c) (i)

Name the other gas evolved in these experiments. ...................................................................................................................................

(ii)

Give a test for this gas. ................................................................................................................................... ................................................................................................................................... [2] 5070/4 S00

For Examiner’s Use

5 For questions 4 to 8 inclusive, place a tick in the box against the best answer.

4

Ethanol may be made by growing yeast in sugar solution. The process is called (a) combustion, (b) cracking, (c) esterification, (d) fermentation. [1]

5

Aqueous barium chloride reacts with aqueous sodium sulphate as shown by the equation BaCl2 + Na2SO4 → BaSO4 + 2NaCl When 0.20 moles of barium chloride was added to 0.40 moles sodium sulphate the number of moles of barium sulphate produced was (a) 0.20, (b) 0.40, (c) 0.60, (d) 0.80. [1]

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For Examiner’s Use

6 6

A student added 5 g of zinc to 50 cm3 of 1.00 mol/dm3 hydrochloric acid at 20 °C. Hydrogen was produced. The experiment was repeated at 30 °C and 40 °C. In each case the total volume of hydrogen produced was plotted against time. Which one of the graphs represents the volumes of hydrogen given off in the three experiments?

40°C 30°C

Volume of hydrogen/ cm3

20°C

0 0

40°C 30°C 20°C

Volume of hydrogen/ cm3

0 0

time/s A

20°C 30°C 40°C

Volume of hydrogen/ cm3

time/s B

Volume of hydrogen/ cm3

20°C 30°C 40°C

0 0

0 0

time/s C

time/s D

(a) A (b) B (c) C (d) D [1]

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7 7

Metal A displaced metal B from a solution of its ions. Metal B displaced metal C from a solution of its ions.

For Examiner’s Use

What could A, B and C have been? A

B

C

(a)

calcium

silver

zinc

(b)

calcium

zinc

silver

(c)

silver

calcium

zinc

(d)

zinc

silver

calcium [1]

8

A student made a polyamide using the apparatus shown below. The polyamide was formed at the junction of the two liquids.

polymer

aqueous solution

non-aqueous solution

The polyamide was (a) nylon, (b) polythene, (c) starch, (d) Terylene. [1]

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8 9

Hydrogen peroxide decomposes slowly at room temperature to form water and oxygen. 2H2O2(aq) → 2H2O(l) + O2(g) A student investigated how the rate of decomposition changes by using two catalysts; copper and manganese(IV) oxide. The volume of oxygen produced was measured at intervals.

10

20

30

40

50

gas syringe

hydrogen peroxide catalyst (a) Experiment 1, using copper powder (Cu). The diagrams below show the volume of oxygen collected in the syringe after the times stated. Further volumes are shown in the table.

10

20

30

40

50

60

10

20

1 min

10

20

30

30

40

50

60

40

50

60

2 min

40

50

60

10

20

3 min

30 4 min

Complete Table 1 for copper by reading the syringes in the diagrams. (b) Experiment 2, using manganese(IV) oxide, MnO2. The experiment was repeated using manganese(IV) oxide as the catalyst in place of copper. The results are shown in Table 1. Table 1 total volume of oxygen/cm3 collected after catalyst

1 min

2 min

3 min

4 min

copper manganese(IV) oxide

9

17

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24

28

5 min

6 min

50

50

32

35

[2]

9 Plot both sets of results from Experiments 1 and 2 on the grid below and draw a smooth curve through each set of points. Label the curves Cu and MnO2.

For Examiner’s Use

60

50

40 total volume of oxygen 30 collected / cm3 20

10

0 0

1

2

3 time / min

4

5

6 [3]

(c) Suggest why the last two readings in Experiment 1 were the same. .......................................................................................................................................... ......................................................................................................................................[1] (d) Use your graph to estimate the time taken, in each experiment, to double the total volume of oxygen produced from 15 cm3 to 30 cm3. Cu

MnO2

time taken to produce 30 cm3/min time taken to produce 15 cm3/min time taken to double the volume/min

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[4]

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10 (e) Which was the better catalyst, copper or manganese(IV) oxide? Explain your answer. .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[2] (f)

Suggest a further experiment which could be done to confirm that the two substances are acting as catalysts. .......................................................................................................................................... ......................................................................................................................................[2]

(g) Suggest another way of increasing the rate of decomposition of hydrogen peroxide without using a catalyst. ......................................................................................................................................[1]

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For Examiner’s Use

11 10 Substance V contains three ions. The following table shows the tests a student did on substance V 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 1

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

2

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

3

observation

For Examiner’s Use

conclusion V is a compound of a transition metal.

NH4+

(b) The mixture from (a) was warmed.

V contains ions.

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

V may contain Fe2+ ions.

(a) To the second part, aqueous ammonia was added until a change was seen.

The presence Fe2+ ions confirmed.

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

of is

4 V contains SO42– ions.

Conclusion: Ions present in V are ......................................................................................[11]

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12 11 A student was given a sample of impure barium hydroxide, Ba(OH)2. She found the percentage purity by titrating an aqueous solution with 0.098 mol/dm3 hydrochloric acid. A sample of barium hydroxide was placed in a weighed container which was reweighed. mass of container + barium hydroxide = 12.16 g mass of container = 9.93 g (a) Calculate the mass of the sample of barium hydroxide. ......................................................................................................................................[1] This sample of barium hydroxide was transferred to a graduated flask and made up to 250 cm3 with distilled water. This was solution G. A pipette was used to transfer 25.0 cm3 of G into a flask. A few drops of methyl orange indicator were added. 0.098 mol/dm3 hydrochloric acid was added from a burette until an end point was reached. (b) What was the colour change of methyl orange? The colour changed from ................................................................................................. to ..................................................................................................................................[2] Three titrations were done. Parts of the burette with the liquid levels before and after each titration are shown below. First Titration

Second Titration

Third Titration 18

0 24

6

42

30 19

1 25

7

43

31 20

2 26

8

44

32

(c) Use the diagram to complete the results table. titration

first

final reading/cm3 first reading/cm3 volume of hydrochloric acid/cm3 best titration results (✓) 5070/4 S00

second

third

For Examiner’s Use

For Examiner’s Use

13 Summary Tick (✓) the best titration results. Using these results, the average volume of hydrochloric acid required was .............cm3. [4] (d) Calculate the number of moles of hydrochloric acid in the average volume of 0.098 mol/dm3 hydrochloric acid. ........................................................................................................................moles

[1]

(e) Ba(OH)2 + 2HCl → BaCl2 + 2H2O Using the equation above and your answer to (d), calculate the number of moles of barium hydroxide in 25.0 cm3 of G.

......................................................................................................................................[1] (f)

Calculate the number of moles of barium hydroxide in the original 250 cm3 of G.

......................................................................................................................................[1] (g) Calculate the mass of one mole barium hydroxide, Ba(OH)2 (Ar: Ba,137; O,16; H,1).

......................................................................................................................................[1] (h) Using your answers to (f) and (g), calculate the mass of barium hydroxide in the 250 cm3 solution G.

......................................................................................................................................[1] (i)

Using your answers to (a) and (h) calculate the percentage purity of the barium hydroxide.

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

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