Formulae of Carboxylic Acids

Specification Point 9.29C:
  • Recall the formulae of molecules of the carboxylic acids, methanoic, ethanoic, propanoic and butanoic acids, and draw the structures of these molecules, showing all covalent bonds
  • Carboxylic acids are a homologous series of compounds that have the general formula of CnH2n+ COOH.
  • They differ by one -CH2 in the molecular formulae from one member to the next.
  • They show a gradation in their physical properties:
    • Boiling points increase with increased carbon chain length.
    • Viscosity increases with increased carbon chain length.
  • They have similar chemical properties.
  • The first four carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.

Carboxylic acids formulae table, Edexcel GCSE Chemistry

Carboxylic Acid Functional Group

Specification Point 9.30C:
  • Recall that the functional group in carboxylic acids is –COOH
  • All carboxylic acids contain the carboxyl functional group (-COOH) which is the part of the acid molecule that is responsible for their characteristic reactions.
  • As with other organic molecules, a large R represents the side chain which doesn´t  affect the chemistry of the molecule.

Carboxylic Acid Functional Group, Edexcel GCSE Chemistry

Diagram showing the -COOH group which characterizes the chemistry of carboxylic acids

  • The carboxylic acids behave like other acids.
  • They dissolve in water and partially ionise producing weakly acidic solutions with pH values of below 7.
  • They react with metals to form salt and water and with carbonates to form a salt, water and carbon dioxide gas.
  • They take part in neutralisation reactions to produce salt and water.
  • Ethanoic acid (also called acetic acid) is the acid used to make vinegar, which contains around 5% by volume ethanoic acid.

Oxidation of Ethanol

Specification Point 9.31C:
  • Recall that ethanol can be oxidised to produce ethanoic acid and extend this to other alcohols (reagents not required)
  • Ethanol can be oxidised using an oxidising agent to produce the carboxylic acid ethanoic acid:

C2H5OH + [O] → CH3COOH + H2O

  • Note that this is an oxidation reaction, not combustion.
  • This reaction occurs when a bottle of wine is left open for a few days as bacteria in the air (acetobacter) use atmospheric oxygen from air to oxidise the ethanol.
  • The acidic, vinegary taste of wine which has been left open for several days is due to the presence of ethanoic acid.
  • The same reaction will occur with any alcohol in the presence of an oxidising agent, producing the corresponding carboxylic acid.
  • E.g. propanol can be oxidised to propanoic acid, hexanol can be oxidised to hexanoic acid etc.

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Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.