• 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 → CuSO_4?+ 5H₂O