Carboxylic acids and esters
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The teaching part (2 min) is free to watch. A free account opens the whole lecture: 2 practice questions, 4 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Vinegar, pear drops and soap
- Making carboxylic acids
- Esterification
Read the transcript of the teaching part
Last time
Before we start: last time, in Aldehydes and ketones, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Vinegar, pear drops and soap
Vinegar is a dilute carboxylic acid, ethanoic acid. Pear drops and banana sweets smell of esters, made from an acid and an alcohol. And soap is made by hydrolysing fats, which are esters, with alkali. One family of reactions links all three.
Making carboxylic acids
Oxidation of a primary alcohol: heat under reflux with excess acidified potassium dichromate(VI). Orange turns green. Oxidation of an aldehyde with the same reagent, or with acidified manganate(VII). Hydrolysis of a nitrile: heat under reflux with dilute acid. CH three CN plus 2 H two O plus H plus goes to CH three COOH plus NH four plus. Hot concentrated acidified manganate(VII) also cleaves alkenes to carboxylic acids.
Esterification
A carboxylic acid reacts with an alcohol, heated with a concentrated sulfuric acid catalyst, to form an ester and water. Ethanoic acid plus ethanol gives ethyl ethanoate plus water: CH three COOH plus C two H five OH in equilibrium with CH three COOC two H five plus H two O. The reaction type is condensation: two molecules join and a small molecule, water, is lost. It is also called esterification. It is reversible. Remove water, or use an excess of one reagent, to increase the yield.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Hydrolysis of esters · Making esters · Reactions as acids.
The whole chapter: Carboxylic Acids and Derivatives, Carboxylic Acids and Derivatives.
Chapter 18: Carboxylic acids and derivatives
- Carboxylic acids and esters 7 min
Also for A Level Chemistry 9701
Which topics come up most in A Level Chemistry 9701 past papers, counted from every paper since 2004: Paper 2 topic frequency, Paper 4 topic frequency.