CAIE Chemistry (9701)

2020 Oct/Nov
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Questions & Answers

Q1bii.
Short Answer 1 mark

State the name of the mechanism in (b)(i).

Model Answer:
Electrophilic substitution
Explanation: This is the mechanism used for nitration of benzene/phenyl compounds in the presence of NO2+.
Q1biii.
Structured 2 marks

Identify the reagents needed to produce NO2+ ions. Write an equation to explain how these reagents produce NO2+ ions.

Model Answer:
Concentrated sulfuric acid and concentrated nitric acid; HNO3 + H2SO4 -> NO2+ + HSO4- + H2O
Explanation: Concentrated sulfuric acid protonates nitric acid, leading to formation of the nitronium ion.
Q1biv.
Short Answer 2 marks

Give reagents and conditions for the production of phenylamine from nitrobenzene in step 2.

Model Answer:
Sn and concentrated HCl, heat under reflux; then add NaOH to liberate phenylamine
Explanation: Nitrobenzene is reduced to phenylamine using tin and hydrochloric acid, followed by alkali to free the amine.
Q1c i.
Short Answer 1 mark

Phenylamine reacts with Br2(aq). Write an equation for this reaction. You may use structural or displayed formulae.

Model Answer:
C6H5NH2 + 3Br2 -> C6H2Br3NH2 + 3HBr
Explanation: Phenylamine undergoes rapid bromination to form 2,4,6-tribromophenylamine.
Q1c ii.
Short Answer 1 mark

Name the organic product of this reaction.

Model Answer:
2,4,6-tribromophenylamine
Explanation: The amino group strongly activates the ring, directing substitution to the 2, 4 and 6 positions.
Q1c iii.
Short Answer 1 mark

Describe two observations that can be seen when phenylamine reacts with Br2(aq).

Model Answer:
Bromine water is decolourised; a white precipitate forms.
Explanation: Phenylamine reacts readily with bromine water, removing its colour and producing insoluble tribromophenylamine.
Q1d.
Structured 3 marks

Describe the relative basicities of ammonia, ethylamine and phenylamine, starting with the least basic. Explain your answer in terms of their structures.

Model Answer:
Phenylamine < ammonia < ethylamine
Explanation: In phenylamine, the lone pair on nitrogen is delocalised into the benzene ring, making it less available to accept H+. Ammonia has a lone pair available for protonation. Ethylamine is most basic because the ethyl group has a +I effect, increasing electron density on nitrogen and making the lone pair more available.
Q1e i.
Short Answer 1 mark

1,3-diaminopropane, H2NCH2CH2CH2NH2, can be used to make polyamides. Identify one compound that would react with 1,3-diaminopropane to form a polyamide.

Model Answer:
A dicarboxylic acid or diacyl chloride, for example hexanedioic acid or hexanedioyl dichloride.
Explanation: Polyamides are formed by condensation between a diamine and a compound with two reactive carboxyl groups or acyl chloride groups.
Q1e ii.
Structured 2 marks

Draw a section of the polymer chain formed from 1,3-diaminopropane and the compound you chose in (e)(i). Your answer should include four monomer residues (two of each type of monomer), show the amide link fully displayed, and clearly identify one repeat unit of this polymer.

Model Answer:
A correct polyamide section showing alternating 1,3-diaminopropane and the chosen dicarboxylic acid/diacyl chloride residues linked by amide bonds, with one repeat unit identified.
Explanation: The polymer must show condensation links of the form -CONH- between the diamine and the dicarboxylic acid/diacyl chloride residues.
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