AQA MERGED QUESTION PAPER AND MARK SCHEME PAPER 3-7405/3 FOR JUNE 2024, Exams of Chemistry

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Friday 21 June 2024 Morning Time allowed: 2 hours

A-level

CHEMISTRY

Paper 3

Section A

Answer all questions in this section.

(^0 1) The structure of 2-hydroxybenzenecarboxylic acid is shown.

(^0 1). 1 Give the equation for the reaction of 2-hydroxybenzenecarboxylic acid with methanol.

In your equation, include the skeletal formula of the organic product. [ 2 marks]

Aspirin is produced from 2-hydroxybenzenecarboxylic acid by reaction with ethanoic anhydride in the presence of concentrated phosphoric acid.

Method

1. Add 2-hydroxybenzenecarboxylic acid to a conical flask.
2. Add excess ethanoic anhydride.
3. Add a few drops of concentrated phosphoric acid.
4. Heat the flask to 85 °C for 10 minutes.
5. Cool the flask and pour the contents into 150 cm 3 of cold water.
6. Filter and wash the impure solid aspirin.
7. Recrystallise the aspirin using a 50:50 mixture of water and ethanol.
8. Check the purity of the aspirin.

(^0 1). 2 Aspirin can also be produced by reacting 2-hydroxybenzenecarboxylic acid with ethanoyl chloride.

State why ethanoic anhydride is preferred to ethanoyl chloride for this preparation. [1 mark]

0 1. (^7) Suggest the identity of two impurities present in the filtered solid aspirin before it is washed in Step 6 of the method. [ 2 marks]

Impurity 1

Impurity 2

(^0 1). 8 Describe the recrystallisation process used to purify the aspirin.

Include the method and apparatus used. [ 6 marks]

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(^0 1). 9 State the physical property that is measured to check the purity of the aspirin.

Describe two ways the result would show that the product is impure. [ 3 marks]

Physical property

1

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0 2. (^2) 20 g of large marble chips is a large excess of calcium carbonate.

Suggest why using a large excess of calcium carbonate means that the rate is only affected by the changing concentration of the hydrochloric acid. [ 1 mark]

(^0 2). 3 The mass of carbon dioxide produced in time t is equal to m t.

The total mass of CO 2 produced during the reaction is equal to m total.

Explain why ( m total – m t) is proportional to the concentration of hydrochloric acid remaining in the flask at time t. [ 2 marks]

Question 2 continues on the next page

Do not write outside the 0 2. (^4) Table 1 shows the rate of reaction, calculated from the gradient of the curve, at^ box five different times.

( m total – m t) is proportional to the concentration of unreacted HCl at time t.

Table 1

Rate of reaction / g s–1^ 23.0 × 10

–4 19.0 × 10–4 15.7 × 10–4 11.5 × 10–4 6.67 × 10–

( m total – m t) / g 0.340^ 0.280^ 0.225^ 0.170^ 0.

On the grid in Figure 2 plot the rate of reaction ( y -axis) against ( m total – m t) ( x -axis). [3 marks]

Figure 2

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Do not write outside the 0 3 The thermal decomposition of but- 3 - en- 1 - ol is investigated at different^ box temperatures ( T ).

CH 2 =CHCH 2 CH 2 OH → CH 2 =CHCH 3 + HCHO

The results from the investigation are used to calculate the rate constant, k , at each temperature.

Table 2 shows some of the results.

Table 2

T / K (^1) T / K–1^ k / s–1^ In k

553 1.81 × 10–3^ 4.6 × 10–4^ –7.

563 1.78 × 10–3^ 8.4 × 10–4^ –7.

573 15.6 × 10–

583 1.72 × 10–3^ 28.0 × 10–4^ –5.

593 1.69 × 10–3^ 49.9 × 10–4^ –5.

(^0 3). 1 Complete Table 2 with the missing values at 573 K [1 mark]

(^0 3). 2 The overall order of the reaction can be deduced from a piece of information in one of the column headings in Table 2.

Identify this piece of information and deduce the overall order. [ 2 marks]

Piece of information

Overall order

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Do not write outside the 0 3. (^3) The Arrhenius equation can be written in the form shown.^ box

In k = In A –

E a RT

On the grid in Figure 3 plot a graph of ln k against (^1) T [ 2 marks]

Figure 3

Question 3 continues on the next page

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Do not write outside the Turn over for the next question^ box

DO NOT WRITE ON THIS PAGE

ANSWER IN THE SPACES PROVIDED

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Do not write outside the 0 4 Figure 4 shows how the pH changes as 0.100 mol dm –3^ sodium hydroxide solution is^ box added to 25.0 cm 3 of 0.0800 mol dm –3^ aqueous propanoic acid at 298 K

Figure 4

(^0 4). 1 Propanoic acid is a weak acid.

State the meaning of weak in this context. [ 1 mark]

(^0 4). 2 Suggest why a student doing an experiment to produce the curve in Figure 4 would add the sodium hydroxide solution dropwise around the equivalence point. [ 1 mark]

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Do not write outside the 0 4. (^5) When sodium hydroxide solution is added to aqueous propanoic acid, the solution^ box formed acts as a buffer when between 5 cm 3 and 15 cm 3 have been added.

Explain why the pH stays approximately constant during this part of the experiment. [ 2 marks]

(^0 4). 6 Methyl orange and universal indicator are not suitable indicators for the titration of solutions of propanoic acid with sodium hydroxide.

State the reason why each indicator is not suitable. [ 2 marks]

Methyl orange

Universal indicator

11

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Do not write outside the 0 5. (^1) Some complexes containing transition metal ions are coloured.^ box

• Explain why some complexes containing transition metal ions are coloured.
• List the factors that affect the colour.
• Describe how colorimetry can be used to determine the concentration of a coloured complex. [ 6 marks]

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Do not write outside the Section B box

Answer all questions in this section.

Only one answer per question is allowed. For each question completely fill in the circle alongside the appropriate answer.

CORRECT METHOD WRONG METHODS

If you want to change your answer you must cross out your original answer as shown.

If you wish to return to an answer previously crossed out, ring the answer you now wish to select as shown.

You may do your working in the blank space around each question but this will not be marked. Do not use additional sheets for this working.

(^0 6) Which row contains two species with different numbers of electrons? [1 mark]

A NH 3 and HF

B CO 3 2–^ and NO 3 –

C H 3 O +^ and HF 2 +

D CH 4 and NH 2 –

0 7 Which element has the highest third ionisation energy? [1 mark]

A Li

B Be

C K

D Ca

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Do not write outside the 0 8 Compound P is converted into compound R by a two-stage synthesis via^ box compound Q.

The yields for the individual steps are:

P → Q 50% Q → R 30%

What is the overall yield of R in this synthesis? [1 mark]

A 15%

B 30%

C 40%

D 80%

(^0 9) What is the formula of ammonium ethanedioate? [1 mark]

A NH 4 (C 2 O 4 ) 2

B (NH 4 ) 2 C 2 O 4

C NH 4 C 2 O 4

D (NH 4 ) 2 (C 2 O 4 ) 3