CIE A Level Chemistry复习笔记1.2.6 Water of Crystallisation

• Water of crystallisation is when some compounds can form crystals which have water as part of their structure
• A compound that contains water of crystallisation is called a hydrated compound
• The water of crystallisation is separated from the main formula by a dot when writing the chemical formula of hydrated compounds
  • Eg. hydrated copper(II) sulfate is CuSO₄∙5H₂O
• A compound which doesn’t contain water of crystallisation is called an anhydrous compound
  • Eg. anhydrous copper(II) sulfate is CuSO₄
• A compound can be hydrated to different degrees
  • Eg. cobalt(II) chloride can be hydrated by six or two water molecules
  • CoCl₂ ∙6H₂O or CoCl₂ ∙2H₂O
• The conversion of anhydrous compounds to hydrated compounds is reversible by heating the hydrated salt

Anhydrous to hydrated salt:

CuSO₄ + 5H₂O → CuSO₄∙5H₂OHydrated to anhydrous salt (by heating):

CuSO₄∙5H₂O → CuSO₄ + 5H₂O