CCEA A Level Chemistry
CCEA A Level Chemistry 5.8 Amides Exam Questions
Free CCEA A Level Chemistry revision for 5.8 Amides: what you need to know, common mistakes and exam-style questions with answers. Covers preparing amides from carboxylic acids and acyl chlorides, hydrolysis, dehydration to nitriles and weak basicity.
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About CCEA A Level Chemistry 5.8 Amides
Section 5.8 of Unit A2 2 is a short section on amides. You need to prepare amides from carboxylic acids and ammonia (via the ammonium salt) and from amines and acyl chlorides, hydrolyse them with acids and alkalis, and dehydrate them with phosphorus pentoxide to form nitriles. You also need to explain why amides are much weaker bases than amines, because the nitrogen lone pair is delocalised into the C=O group. Amides link several sections: carboxylic acids (4.8), acyl chlorides (4.9), amines (5.7), the peptide link in amino acids and proteins (5.9) and polyamides such as nylon (5.10). Questions often appear inside reaction scheme or synthesis problems.
What you need to know
- Structure Amides contain -CONH2 (primary amides) or -CONHR (N-substituted amides), for example ethanamide CH3CONH2.
- From carboxylic acids Ethanoic acid reacts with ammonia to give ammonium ethanoate; heating this salt removes water to give ethanamide: CH3COONH4 gives CH3CONH2 + H2O.
- From acyl chlorides Acyl chlorides react readily with ammonia or amines, for example CH3COCl + CH3NH2 gives CH3CONHCH3 + HCl (the HCl reacts with excess amine).
- Hydrolysis Heating with dilute acid gives the carboxylic acid and an ammonium salt; heating with alkali gives the carboxylate salt and ammonia (or an amine), which can be detected with damp red litmus.
- Dehydration Heating a primary amide with phosphorus pentoxide (P4O10) removes water to form a nitrile: CH3CONH2 gives CH3CN + H2O.
- Basicity The lone pair on N is delocalised over the N-C=O group, so it is much less available to accept a proton. Amides are therefore very weak bases, approximately neutral.
Common mistakes in 5.8 Amides
- Saying amides are basic like amines. The lone pair is delocalised into C=O, so amides are almost neutral.
- Forgetting the ammonium salt intermediate. The acid and ammonia first form a salt, which is then heated to give the amide.
- Writing the wrong products of alkaline hydrolysis. You get the carboxylate salt and ammonia, not the carboxylic acid.
- Confusing dehydration of amides with hydration. P4O10 removes water to form a nitrile.
- Drawing the amide link as C-O-N. The link is -CO-NH-, with nitrogen bonded directly to the carbonyl carbon.
Try three 5.8 Amides exam-style questions
1. Write equations for the hydrolysis of ethanamide by sodium hydroxide and by hydrochloric acid. (2 marks)
Show the mark scheme answer
CH3CONH2 + NaOH gives CH3COONa + NH3; CH3CONH2 + HCl + H2O gives CH3COOH + NH4Cl.
2. Explain why ethanamide is a much weaker base than ethylamine. (2 marks)
Show the mark scheme answer
In ethanamide the nitrogen lone pair is delocalised into the C=O group; so it is less available to accept a proton.
3. Give the reagent and product when propanamide is dehydrated. (2 marks)
Show the mark scheme answer
Phosphorus pentoxide (P4O10); propanenitrile, CH3CH2CN.
5.8 Amides FAQs
What does CCEA A Level Chemistry 5.8 Amides cover?
It covers preparing amides from carboxylic acids and acyl chlorides, hydrolysis, dehydration to nitriles and why amides are weak bases.
Which unit is 5.8 Amides examined in?
It is examined in Unit A2 2: Analytical, Transition Metals, Electrochemistry and Organic Nitrogen Chemistry, a 2 hour paper with a multiple-choice section and structured questions. Related practical skills can also be assessed in Unit A2 3.
How do amides fit into synthesis questions?
They link acids, acyl chlorides, nitriles and amines. Learn the reagents for each conversion so you can plan two or three step routes.
