1.23 understand how the formulae of simple compounds can be obtained experimentally, including metal oxides, water and salts containing water of crystallisation

FORMULAE:

- 1. Find the mass of the multiple compounds.
- 2. Calculate the moles of water lost. That is mass / Mr.
- 3. Calculate the moles of anhydrous salt made. That is mass / Mr.
- 4. Work out ratio of anhydrous and water. Must be a whole number, e.g. if you get 0.02 moles of X and 0.01 moles of Y the ratio would be 2X : 1Y (since 0.02 / 0.01)

Another example: (thank you - http://www.docbrown.info/page04/4_73calcs14other4.htm)

Calculate the % of water in hydrated magnesium sulphate MgSO₄.7H₂O salt crystals

- Relative atomic masses: Mg = 24, S = 32, O = 16 and H = 1
- relative formula mass = 24 + 32 + (4 x 16) + [7 x (1 + 1 + 16)] = 246
- 7 x 18 = 126 is the mass of water
- so % water = 126 x 100 / 246 = 51.2%