AQA A Level Chemistry

Revision Notes

7.3.1 Carboxylic Acids

Carboxylic Acids

Carboxylic acids

  • Carboxylic acid is the name given to the family of compounds that contain the carboxyl functional group, -COOH
  • The general formula of a carboxylic acid is CnH2n+1COOH which can be shortened to just RCOOH
    • (In some countries, this family is also called alkanoic acid)
  • The nomenclature of carboxylic acid follows the pattern alkan + oic acid, e.g. propanoic acid
  • There is no need to use numbers in the name as the carboxyl group, COOH, is always on the number 1 carbon atom

Carboxylic Acids Examples Table

Carboxylic Acids Examples Table, downloadable AS & A Level Chemistry revision notes

Weak Acids

  • Carboxylic acids with fewer than six carbon atoms per molecule are water-soluble
    • This is because water molecules can hydrogen-bond with the functional group
  • In aqueous solution they are only slightly ionised, to give low concentrations of hydronium ions and alkanoate ions (often called carboxylate ions)

Weak acids, downloadable AS & A Level Chemistry revision notes

Carboxylic acids are weak acids that do not fully dissociate in water, the position of the equilibrium lies to the left

  • This partial ionisation in solution means that carboxylic acids are weak acids
  • This means that the position of the equilibrium lies to the left and that the concentration of H+ is much smaller than the concentration of the carboxylic acid
  • However, the concentration of hydrogen ions is sufficient to react with an aqueous solution of sodium carbonate or sodium hydrogen carbonate to produce carbon dioxide
  • These reactions are a useful test for the possible presence of a carboxylic acid:
    • Sodium carbonate: 2RCOOH + Na2CO3 → 2RCOONa+ + CO2 + H2O
    • Ionic equation with carbonates: 2RCOOH + CO32- → 2RCOO+ CO2 + H2O
    • Sodium hydrogen carbonate: RCOOH + NaHCO3 → RCOONa+ + CO2 + H2O
    • Ionic equation with hydrogen carbonates: RCOOH + HCO3 → RCOO+ CO2 + H2O

Preparation of esters

  • Esters are formed from the condensation reaction between an alcohol and carboxylic acid in the presence of a concentrated strong acid catalyst e.g. sulfuric or hydrochloric acid
  • This reaction is often referred to as esterification
  • A condensation reaction involves the elimination of a small molecule not always water
    • Esterification is one example of a condensation reaction as water is eliminated from the acid and alcohol reacting together

Hydroxy Compounds Esterification of Alcohols, downloadable AS & A Level Chemistry revision notes

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