Changes described in observations include:

  • The colour and odour of any gas produced
  • The change in colour of a solution
  • The dissolving or precipitation of a solid
  • The colour of solids precipitated
  • The appearance or disappearance of an odour
  • Any other changes in appearance
  • Change in temperature

3 types: Acrid, Pungent and Foul

Acrid – Acids (easy to remember) – as a general rule, acidic oxides or acids, because molecules hydrolyse to form acids in your nose. e.g. HCl, SO3, NO2

Pungent – ammonia, most nitrogen compounds. Rotten fish.

Foul – sewage, rotten eggs smell, H2S




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