O Level Chemistry 5070 Paper 41, Oct/Nov 2024

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Question paper

5070/41 · Oct/Nov 2024

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A teacher investigates the electrolysis of molten lead(II) bromide. Lead(II) bromide is a solid at room temperature. Fig. 1.1 shows the apparatus the teacher uses.

Name the pieces of apparatus labelled L and M. Suggest the material from which L and M are made. name ......................................................................................................................................... material .....................................................................................................................................

[2]

Describe the appearance of the products at L and at M. appearance of product at L ...................................................................................................... appearance of product at M ......................................................................................................

[2]

The teacher stops heating and allows the lead(II) bromide to cool. Explain why the lamp goes out.

[2]

A student titrates four samples of $0.800 {mol/dm}^{3}$ aqueous sodium hydroxide, $NaOH(aq)$ , with aqueous ethanedioic acid. In titration 1 the student: • rinses and fills a burette with aqueous ethanedioic acid • uses a volumetric pipette to add $25.0 {cm}^{3}$ of $NaOH(aq)$ to a conical flask • adds thymolphthalein indicator to the conical flask • places the conical flask on a white tile • adds aqueous ethanedioic acid from the burette while swirling the flask, adding drop by drop near the end-point, until the solution just changes colour. The student repeats the titration three more times.

Fig. 2.1 shows the burette readings for two of the titrations. Record the burette readings in Table 2.1. Complete Table 2.1.

[3]

Tick (✓) the two best titration results in Table 2.1.

[1]

Use the ticked (✓) titration results in Table 2.1 to calculate the average volume of aqueous ethanedioic acid needed to neutralise $25.0 {cm}^{3}$ of the aqueous sodium hydroxide. volume .................................................. ${cm}^{3}$

[1]

Calculate the number of moles of $NaOH$ in $25.0 {cm}^{3}$ of $0.800 {mol/dm}^{3}$ $NaOH(aq)$ . number of moles .........................................................

[1]

One mole of ethanedioic acid is neutralised by two moles of sodium hydroxide. Use your answers to (c) and (d) to calculate the concentration, in ${mol/dm}^{3}$ , of ethanedioic acid. Give your answer to three significant figures. concentration ........................................... ${mol/dm}^{3}$

[3]

f(i)

The formula of ethanedioic acid is $C_{2} H_{2} O_{4} \cdot n H_{2} O$ . $100 {cm}^{3}$ of the aqueous ethanedioic acid contains $6.3 g$ of $C_{2} H_{2} O_{4} \cdot n H_{2} O$ . Use your answer from (e) to calculate the relative formula mass, $M_{r}$ , of $C_{2} H_{2} O_{4} \cdot n H_{2} O$ . $M_{r}$ .........................................................

[2]

f(ii)

Use your answer from (f)(i) to deduce the value of $n$ in $C_{2} H_{2} O_{4} \cdot n H_{2} O$ . Give your answer to the nearest whole number. [ $A_{r}$ : $H$ , 1; $C$ , 12; $O$ , 16] $n$ .........................................................

[1]

State why the conical flask is placed on a white tile before aqueous ethanedioic acid is added from the burette.

[1]

State why a measuring cylinder is not used to measure $25.0 {cm}^{3}$ of $NaOH(aq)$ in this experiment.

[1]

A student investigates solid Y and solution Z.

a(i)

Solid Y is a white powder. The tests the student does on Y are shown in Table 3.1. Some of the observations for these tests are also shown. Describe how the gas is passed through limewater in test 1. You may draw a labelled diagram to help answer the question.

[1]

a(ii)

Describe two other observations the student makes in test 1. 1. ....................................................................................................................................... 2. .......................................................................................................................................

[2]

a(iii)

Identify the gas produced in test 1.

[1]

a(iv)

Y contains one anion. Use the observations from test 1 to identify this anion.

[1]

a(v)

Use the observations from test 2 to identify the dilute acid used in test 1.

[1]

a(vi)

Identify the cation in Y using the observations from tests 3 and 4.

[1]

b(i)

Solution Z is colourless. The student thinks that Z contains ${Cu}^{2 +}$ ions. State why the student is not correct.

[1]

b(ii)

Solution Z contains $K^{+}$ ions. Describe how to do a flame test on solution Z to confirm the identity of this cation.

[3]

b(iii)

Solution Z contains ions of a Group VII element. Describe a test and the possible results to identify which Group VII ion is present in Z.

[3]

Argentan is an alloy containing only zinc, nickel and copper. Zinc and nickel both react with dilute hydrochloric acid. Copper does not react with dilute hydrochloric acid. Plan an investigation to find the percentage by mass of copper in a powdered sample of argentan. Your plan must include the use of common laboratory apparatus, argentan and dilute hydrochloric acid. No other chemicals should be used. Your plan must include: • the apparatus needed • the method to use and the measurements to take • procedures to ensure that the percentage determined is as accurate as possible • how the measurements are used to determine the percentage by mass of copper in the sample. You may draw a diagram to help answer the question.

[6]

Mark scheme

5070/41 · Oct/Nov 2024

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1a · 2 marks

M1
electrode(s)
M2
carbon / graphite / platinum

1b · 2 marks

M1
shiny / black / grey / silver solid / liquid (deposit of lead)
M2
orange / brown vapour / gas (of bromine)

1c · 2 marks

M1
solidifies
M2
current cannot flow

2a · 3 marks

M1
correct values for both initial and both final readings completed
M2
all readings to 1 decimal place (including 0.0)
M3
all volumes calculated correctly

2b · 1 mark

1 mark
two ticks for the two values which are closest together from 2a

2c · 1 mark

1 mark
correct average of the ticked values from 2b

2d · 1 mark

1 mark
0.02

2e · 3 marks

M1
2d / 2
M2
M1 / 2c × 1000 correctly evaluated to any sf ignoring rounding errors
M3
answer correct to 3 sf

2f(i) · 2 marks

M1
63 g/dm3 OR 2e × 0.1 OR 6.3 / 2e
M2
(M1 ÷ 2e =) 126 OR (6.3 / M1 =) 126 OR M1 × 10

2f(ii) · 1 mark

1 mark
(2fi – 90) ÷ 18

2g · 1 mark

1 mark
to see colour change (more) easily / clearly

2h · 1 mark

1 mark
(measuring cylinder) is not accurate / precise enough

3a(i) · 1 mark

1 mark
description / diagram of how gas bubbled through limewater using pipette / delivery tube

3a(ii) · 2 marks

M1
solid dissolves / disappears
M2
effervescence

3a(iii) · 1 mark

1 mark
carbon dioxide

3a(iv) · 1 mark

1 mark
carbonate

3a(v) · 1 mark

1 mark
sulfuric acid

3a(vi) · 1 mark

1 mark
Zn2+

3b(i) · 1 mark

1 mark
because the solution is colourless / Cu2+(aq) are blue

3b(ii) · 3 marks

M1
dip wire / splint into solution / Z
M2
put in blue / roaring / non-luminous flame (of Bunsen burner)
M3
observe colour (of flame) produced / (flame turns) lilac / purple

3b(iii) · 3 marks

M1
add (dilute) nitric acid
M2
add (aqueous) silver nitrate
M3
observe if white, cream or yellow precipitate produced

4 · 6 marks

M1
uses a suitable named reaction container
M2
weigh (fixed mass of) Argentan metal (on balance)
M2
add hydrochloric acid
M2
filter (to remove unreacted copper)
M2
weigh copper
M3
wait until effervescence ends / use excess hydrochloric acid
M3
wash and dry copper
M3
repeat and average
M4
percentage copper = mass of copper / mass of Argentan metal × 100%

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