Determining Formula

• Water of crystallisation assumptions


  1. All of the water has been lost (Only surface of crystal can be seen- solution is to heat to a constant mass)
  2. No further decomposition
• Experimental Determination of num of moles of water of crystallisation present


  1. Weigh empty crucible and record its mass
  2. Add hydrated salt. Reweight crucible and record mass
  3. Place crucible onto clay triangle and gently heat with a loose-fitting lid (solid doesn't escape but water vapour can)
  4. Allow to cool and reweight contents
  5. Reheat and reweigh until constant mass is observed (heating to a constant mass)