Edexcel International A Level Chemistry
Edexcel International A Level Chemistry Carboxylic Acid Derivatives Exam Questions
Free Edexcel International A Level Chemistry exam questions for Carboxylic Acid Derivatives, with a mark scheme for every pack. Covers acyl chlorides, esters, reactions with water, alcohols, ammonia and amines, ester hydrolysis in acid and alkali, and polyesters.
Carboxylic Acid Derivatives exam questions
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About Edexcel International A Level Chemistry Carboxylic Acid Derivatives
Carboxylic acid derivatives in Unit 4 of Edexcel International A Level Chemistry covers acyl chlorides and esters, compounds in which the OH of a carboxylic acid has been replaced. Acyl chlorides are highly reactive and react vigorously with water, alcohols, ammonia and amines, making them useful in synthesis. Esters are hydrolysed by acids or alkalis, and condensation polymerisation produces polyesters. This topic follows Carboxylic acids and connects to Organic nitrogen compounds in Unit 5, where acyl chlorides make amides. Examiners test equations and observations for acyl chloride reactions, the products of acid and alkaline hydrolysis, and drawing polyester repeat units.
What you need to know
- Acyl chlorides with water Acyl chlorides react rapidly with water at room temperature to give a carboxylic acid and steamy fumes of HCl, for example CH3COCl + H2O gives CH3COOH + HCl.
- Acyl chlorides with alcohols They react with alcohols to give esters and HCl. This is faster and goes to completion, unlike the reversible acid-catalysed esterification of carboxylic acids.
- Acyl chlorides with ammonia and amines With concentrated ammonia they give primary amides, and with primary amines they give N-substituted amides, for example CH3COCl + CH3NH2 gives CH3CONHCH3 + HCl.
- Ester hydrolysis Acid hydrolysis (dilute acid, reflux) is reversible and gives the carboxylic acid and alcohol. Alkaline hydrolysis (NaOH, reflux) goes to completion and gives the carboxylate salt and alcohol.
- Polyesters A dicarboxylic acid (or diacyl chloride) and a diol undergo condensation polymerisation, eliminating water (or HCl) to form ester links, as in PET.
- Naming Esters are named alkyl alkanoate, with the alcohol part first, for example ethyl ethanoate from ethanol and ethanoic acid. Acyl chlorides end in -oyl chloride, such as ethanoyl chloride.
Common mistakes in Carboxylic Acid Derivatives
- Naming esters the wrong way round, such as ethanoyl ethyl. The alkyl group from the alcohol comes first: methyl propanoate comes from methanol and propanoic acid.
- Saying alkaline ester hydrolysis gives a carboxylic acid. It gives the carboxylate salt, which needs acidifying to obtain the acid.
- Forgetting HCl as a product of acyl chloride reactions, or forgetting that with ammonia the HCl reacts with more ammonia to form NH4Cl.
- Drawing polyester repeat units with an extra OH or H at the ends. A repeat unit has open bonds at each end.
- Describing acyl chloride reactions as slow or needing a catalyst. They are vigorous at room temperature.
Try three Carboxylic Acid Derivatives exam-style questions
1. Write an equation for the reaction of propanoyl chloride with ethanol and name the organic product. (2 marks)
Show the mark scheme answer
CH3CH2COCl + CH3CH2OH gives CH3CH2COOCH2CH3 + HCl; ethyl propanoate.
2. Methyl ethanoate is heated under reflux with aqueous sodium hydroxide. Name the products and explain why this method is preferred to acid hydrolysis when a high yield is needed. (3 marks)
Show the mark scheme answer
Sodium ethanoate and methanol; alkaline hydrolysis is not reversible (carboxylate ion does not react with alcohol); so the reaction goes to completion.
3. Draw the repeat unit of the polyester formed from benzene-1,4-dicarboxylic acid and ethane-1,2-diol and name the small molecule eliminated. (3 marks)
Show the mark scheme answer
Repeat unit: -OC-C6H4-CO-O-CH2CH2-O- with ester links drawn correctly; open bonds at each end; water is eliminated.
Carboxylic Acid Derivatives FAQs
What does Edexcel International A Level Chemistry Carboxylic acid derivatives cover?
It covers acyl chlorides and their reactions with water, alcohols, ammonia and amines, esters and their acid and alkaline hydrolysis, and polyesters formed by condensation polymerisation.
Which unit is Carboxylic acid derivatives examined in?
It is part of Unit 4, and acyl chloride reactions are needed again in Unit 5 for amides and synthesis routes.
How do I remember acyl chloride reactions?
Use one pattern: acyl chloride plus a molecule with an N to H or O to H bond gives a product where the Cl is replaced, plus HCl. Practise with water, alcohols, ammonia and amines.
