Carboxylic Acids (Edexcel GCSE Chemistry)

Revision Note

Stewart Hird

Last updated

Carboxylic Acids

  • Carboxylic acids is the name given to compounds containing the functional group carboxyl, -COOH

  • The naming of a carboxylic acid follows the pattern alkan + oic acid

  • The names and structure of the first four carboxylic acids are shown below

The Names and Structures of the First Four Carboxylic Acids

Carboxylic acids table, IGCSE & GCSE Chemistry revision notes

Examiner Tips and Tricks

Vinegar is an aqueous solution of ethanoic acid and contains about 5% of the acid by volume.

Making Ethanoic Acid

Preparation of ethanoic acid

  • Alcohols undergo oxidation to produce carboxylic acids when treated with oxidising agents

  • When ethanol is heated with acidified potassium dichromate solution the ethanol oxidises to ethanoic acid

  • The equation for the reaction is:

CH3CH2OH + [O]  →  CH3COOH + H2O

  • The oxidising agent is represented by the symbol for oxygen in square brackets

  • The reaction is slow so the mixture is heated to its boiling point for about an hour; to avoid the substances evaporating a condenser is placed above the reaction flask that prevents volatile liquids from escaping

  • During the reaction the potassium dichromate turns from orange to green

Heating under Reflux (1), downloadable IB Chemistry revision notes

Ethanol can be oxidised by heating it with potassium dichromate in sulfuric acid. The solution turns  from orange to green during the reaction

Examiner Tips and Tricks

Other carboxylic acids can be prepared from the oxidation of corresponding alcohols with the same carbon chain length.

Predicting Products

  • Organic molecules that belong to the same homologous series react in the same way, so the products of those reactions can be predicted

  • Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group

  • All members of a homologous series have:

    • The same general formula

    • The difference in the molecular formula between one member and the next is CH2

    • Gradation in their physical properties

    • Same functional group

    • Similar chemical properties

  • The chemistry of homologous series is therefore determined by the functional group

  • We can use this to predict how other molecules in a homologous series will react

  • Previously we have seen that ethanol can be oxidised to ethanoic acid using acidified potassium dichromate

  • The next member of the series is propanol, so we can predict the reaction would be:

CH3CH2CH2OH + [O]  →  CH3CH2COOH + H2O

      propanol                   propanoic acid

  • Although the homologous series allows us to predict what the reaction products should be, it tells us nothing about the rate or extent of the reaction

  • For example, as the chain length increases in alcohols the combustion or oxidation reactions may be slower or incomplete as the carbon chain influences the reactivity of the functional group

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.