How do carboxylic acids behave as acids, and how are esters and acyl derivatives made and broken?
Acidity of carboxylic acids and their reactions with metals, alkalis and carbonates; esterification and ester hydrolysis (acid and alkaline); and the reactions of acyl chlorides and acid anhydrides.
An OCR H432 module 6 answer on carboxylic acids and esters: acidity and reactions with metals, alkalis and carbonates, esterification and acid and alkaline ester hydrolysis, and the reactions of acyl chlorides and acid anhydrides.
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What this topic is asking
OCR specification point 6.1.3 wants you to explain the acidity of carboxylic acids and their reactions with metals, alkalis and carbonates, describe esterification and the acid and alkaline hydrolysis of esters, and give the reactions of the more reactive acyl chlorides and acid anhydrides. This completes the oxygen-containing functional groups.
Acidity of carboxylic acids
Esterification
Ester hydrolysis
Acyl chlorides and acid anhydrides
Examples in context
Example 1. Esters as flavourings and solvents. Many esters have fruity smells and are used as artificial flavourings and as solvents (for example in nail-varnish remover), all made by the esterification or acyl-chloride routes covered here.
Example 2. Soap from saponification. Alkaline hydrolysis of the ester links in animal or vegetable fats produces the sodium salts of long-chain carboxylic acids, which are soap, a direct industrial use of saponification.
Try this
Q1. State the observation when a carboxylic acid is added to sodium carbonate, and what it confirms. [2 marks]
- Cue. Effervescence (bubbles of carbon dioxide); it confirms the carboxylic acid group.
Q2. Name the organic product when ethanoyl chloride reacts with methanol. [1 mark]
- Cue. Methyl ethanoate (an ester).
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksEthanoic acid reacts with ethanol. (a) Name the type of reaction and the catalyst. (b) Name the organic product and write the equation. (c) State how the yield could be increased.Show worked answer →
(a) Esterification (a condensation reaction), catalysed by concentrated sulfuric acid (heated under reflux) (1).
(b) The product is ethyl ethanoate: (1)(1).
(c) Because the reaction is an equilibrium, the yield is increased by using an excess of one reactant or by removing the ester or water as it forms (1).
Markers reward the reaction type and catalyst, the named ester and balanced equation, and a valid way to shift the equilibrium towards the ester.
OCR 20214 marksEthanoyl chloride reacts with (a) water, (b) ethanol and (c) ammonia. For each, name the organic product and state the other product.Show worked answer →
(a) With water: ethanoic acid, plus hydrogen chloride (HCl) (1).
(b) With ethanol: ethyl ethanoate (an ester), plus hydrogen chloride (1).
(c) With ammonia: ethanamide (an amide), plus hydrogen chloride (which reacts with excess ammonia to form ammonium chloride) (1)(1).
Markers reward the correct organic product in each case (acid, ester, amide) and the release of hydrogen chloride as the other product.
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Sources & how we know this
- OCR A-Level Chemistry A (H432) specification — OCR (2015)