Alcohol and carboxylic acid

• Alcohols

  Organic compounds which have the hydroxyl (-OH) functional group

  
• Alcohols

  • Methanol (CH3OH)
  • Ethanol (C2H5OH)
  • Propanol (C3H7OH)
• Alcohols

  • Contain carbon, hydrogen, and oxygen
  • Have the general molecular formula CnH2n+1OH (where n = 1, 2, 3, etc.)
  • Their names end with '-ol'
• Physical properties of alcohols

  • Volatile liquids at room temperature and pressure
  • Generally soluble in water
  • Higher melting and boiling point than hydrocarbons with same number of carbon atoms
• As the molecular size of alcohols increases


  • Solubility of alcohols decreases
  • Boiling and melting points of alcohols increases
• Although alcohols contain the -OH group, they are not alkalis. In fact, they are all neutral.
• Combustion of alcohols

  1. Complete combustion: Alcohols burn in excess air (oxygen) to produce carbon dioxide and water vapour

  2. Incomplete combustion: Alcohol burns in limited supply of air to produce carbon monoxide, water vapour and soot

  
• Oxidation of alcohols

  Alcohols are oxidised to carboxylic acids when heated with oxidising agents such as acidified potassium manganate (VII)

  
• Oxidising agents

  • (purple) potassium manganate (VII)
  • (orange) potassium dichromate (VI)
  • Bacteria in the air (oxygen)
• Producing ethanol by fermentation of glucose


  1. Glucose solution is mixed with yeast and kept at 37°C

  2. Carbon dioxide is produced during fermentation

  3. A dilute solution of ethanol (15% alcohol) is usually produced

  4. Ethanol can be extracted by fractional distillation of the dilute solution

  
• Fermentation takes place only in the absence of oxygen, so the flask must be tightly stoppered/airtight
• If the temperature is raised beyond 37 C, the enzymes will be denatured, and fermentation will stop
• Carboxylic acids

  A homologous series of organic compounds which have the carboxyl (-COOH) functional group

  
• Carboxylic acids

  • Methanoic acid (HCOOH)
  • Ethanoic acid (CH3COOH)
  • Propanoic acid (C2H5COOH)

  
• Carboxylic acids

  • Have the general formula CnH2n+1 COOH (n starts from 0)
  • Their names end with '-oic acid'
• Where carboxylic acids can be found

  • Malic acid in green apples
  • Tartaric acid in grapes
  • Citric acid in citrus fruits
  • Methanoic acid in ant bites
  • Some types in humans' sweat
• Physical properties of carboxylic acids

  • Very soluble in water due to the carboxyl group (-COOH)
  • Have relatively high melting and boiling points, hence are liquids at room temperature and pressure
  • Weak acids
• Producing ethanoic acid from ethanol

  1. Oxidation by acidified potassium manganate (VII): Potassium manganate (VII) acts as an oxidising agent and is reduced, its colour changes from purple to colourless

  2. Oxidation by atmospheric oxygen: In the presence of certain bacteria, atmospheric oxygen oxidises ethanol to ethanoic acid