What are Carboxylic Acids? (Edexcel IGCSE Chemistry)

The Carboxylic Acids

Spec point — 8.6C

Carboxylic acids

• Carboxylic acids is the name given to compounds containing the functional group carboxyl, -COOH
• The general formula of a carboxylic acid is C_nH_2n+1COOH which can be shortened to just RCOOH

Carboxylic acid functional group

Diagram of the general structure of a carboxylic acid. The R- represents a varying hydrocarbon chain

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

The structures and formulae of the first four carboxylic acids

• The formula for each carboxylic acid is:

  • Methanoic acid- HCOOH
  • Ethanoic acid- CH₃COOH
  • Propanoic acid- CH₃CH₂COOH
  • Butanoic acid- CH₃CH₂CH₂COOH

Exam Hint The carbon atom in the -COOH functional group is counted as part of the molecule and not just the functional group. E.g. CH₃CH₂CH₂COOH has 4 carbon atoms so is called butanoic acid, not propanoic acid.