carboxylic acids

• carboxylic acids have the functional group -COOH
• the first 4 members of a homologous series of carboxylic acids are:

  • methanoic acid - HCOOH
  • ethanoic acid - CH3COOH
  • propanoic acid - C2H5COOH
  • butanoic acid - C3H7COOH
• (in water) carboxylic acids are weak acids

  have pH less than 7
• reaction with water

  ethanoic acids <--> ethanoate ion + H+
• ethanoic acid <--> ethanoate ion + h+

  • ethanoic acid is IONISING to form H+ ions and negative ions e.g. ethanoic ion
  • reversible reaction, the position of equilibrium lies on the left
  • most molecules stay as they are and only a small proportion ionise = WEAK ACID
• react with carbonates to form:

  • salt
  • carbon dioxide
  • water
• ethanoic acid + sodium carbonate --> sodium ethanoate + carbon dioxide + water
• esters are compounds formed when a carboxylic acid reacts with an alcohol, and we also make water
• esters general equation:

  carboxylic acid + alcohol <--> ester + water
• ester equation w product ethyl ethanoate

  ethanoic acid + ethanol <--> ethyl ethanoate + water

  • requires sulphuric acid as a catalyst
  • reversible reaction, prevented as the ester is distilled off as soon as it forms
• Ethanoic acid ionises in water.

  The equation for the reaction is:

  CH3COOH(aq) ⇌ CH3COO–(aq) + H+(aq)

  Explain how the equation shows that ethanoic acid is a weak acid (2 marks)

  • partial ionisation
  • because the reaction is reversible