OxfordAQA International A Level Chemistry
OxfordAQA International A Level Chemistry 3.3.11 Amines Exam Questions
Free OxfordAQA International A Level Chemistry revision for 3.3.11 Amines: what you need to know, common mistakes and exam-style questions with answers. Covers making amines, base strength, nucleophilic substitution, quaternary ammonium salts and reactions with acyl chlorides.
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About OxfordAQA International A Level Chemistry 3.3.11 Amines
Amines is an A2 organic topic examined in Unit 4. You need to describe how primary aliphatic amines are made from halogenoalkanes and ammonia, or by reducing nitriles, and how aromatic amines are made by reducing nitro compounds, with their use in making dyes. You also need to explain the relative base strengths of ammonia, primary aliphatic amines and primary aromatic amines in terms of lone pair availability. Amines act as nucleophiles to form secondary and tertiary amines and quaternary ammonium salts, which are used as cationic surfactants, and they react with acyl chlorides by nucleophilic addition-elimination. It links to halogenoalkanes, aromatic chemistry and amino acids.
What you need to know
- Making aliphatic amines Halogenoalkanes react with excess ammonia to give primary amines, though further substitution gives a mixture. Reducing nitriles, for example with LiAlH4 or with hydrogen and a nickel catalyst, gives a primary amine only.
- Making aromatic amines Nitrobenzene is reduced to phenylamine using tin and concentrated hydrochloric acid. Aromatic amines are used to make dyes.
- Base strength Amines are bases because the nitrogen lone pair accepts a proton. Primary aliphatic amines are stronger bases than ammonia because alkyl groups release electrons; aromatic amines are weaker because the lone pair is delocalised into the ring.
- Nucleophilic substitution Amines are nucleophiles, so a primary amine reacts with a halogenoalkane to give a secondary amine, then a tertiary amine and finally a quaternary ammonium salt.
- Quaternary ammonium salts Quaternary ammonium salts with long alkyl chains are used as cationic surfactants in fabric softeners and hair conditioners.
- Reaction with acyl chlorides Amines react with acyl chlorides by nucleophilic addition-elimination to form N-substituted amides.
Common mistakes in 3.3.11 Amines
- Saying phenylamine is a stronger base than ammonia. The lone pair is delocalised into the ring, making it less available, so it is weaker.
- Forgetting that excess ammonia is needed to favour a primary amine from a halogenoalkane.
- Explaining base strength without mentioning the lone pair on nitrogen.
- Writing that quaternary ammonium ions can act as bases. They have no lone pair on nitrogen.
Try three 3.3.11 Amines exam-style questions
1. Rank ammonia, ethylamine and phenylamine in order of base strength, strongest first, and explain the position of ethylamine. (3 marks)
Show the mark scheme answer
Ethylamine > ammonia > phenylamine; the ethyl group is electron releasing; so the lone pair on nitrogen is more available to accept a proton.
2. Give the reagents to convert nitrobenzene into phenylamine. (2 marks)
Show the mark scheme answer
Tin and concentrated hydrochloric acid; followed by sodium hydroxide.
3. Explain why reducing a nitrile is a better way than using ammonia to make a pure primary amine. (2 marks)
Show the mark scheme answer
Halogenoalkane and ammonia give further substitution to secondary and tertiary amines; nitrile reduction gives only the primary amine.
3.3.11 Amines FAQs
What does OxfordAQA International A Level Chemistry 3.3.11 Amines cover?
It covers making amines, base strength, nucleophilic substitution, quaternary ammonium salts and reactions with acyl chlorides.
Which unit is 3.3.11 Amines examined in?
It is examined in Unit 4, an International A2 paper covering organic and physical chemistry. The Unit 5 practical and synoptic paper can also assess it.
Why are quaternary ammonium salts useful as surfactants?
They have a positively charged head and long hydrocarbon tails. The positive head sticks to negatively charged surfaces such as fabric or hair, so they are used as cationic surfactants in fabric softeners and conditioners.
