Physical properties of Aldehydes and Ketones

Physical properties of Aldehydes and Ketones :

  • Methanal - Gas at room temperature
  • Ethanal - Volatile liquid
  • Other aldehydes and ketones - Liquid or solid at room temperature
  • Boling points of aldehydes and ketones are higher than those of hydrocarbons and ethers of comparable molecular masses.

           Reason : Weak molecular association in aldehydes and ketones, arising out of the dipole-dipole interactions

  • Boiling points of aldehydes and ketones are lower than those of alcohols of similar molecular masses.

         Reason : Absence of intermolecular hydrogen bonding

  • Lower members of aldehydes and ketones are miscible with water in all proportions.

           Reason : They form hydrogen bonds with water.

         

  • Solubility of aldehydes and ketones decreases rapidly on increasing the length of the alkyl chain.
  • All aldehydes and ketones are fairly soluble in organic solvents such as ether, methanol, etc.
  • Lower aldehydes have sharp pungent odours.
  • As the size of aldehydes increases, the odour becomes less pungent and more fragrant.