Water of Crystallisation Some compounds have water associated with them. Eg. Cobalt chloride CoCl2 in crystal form is really cobalt chloride CoCl2.6H2O For each CoCl2 there are 6 H2O molecules in the crystal When we heat the pale pink crystals to remove the water the crystals lose weight and turn blue The water that is included in these compounds is called the water of crystallisation, that is the water included in the crystals
Calculating water of crystallisation • Weigh the hydrous salt • Dehydrate the salt • Weigh the anhydrous salt • Calculate the molar mass of the anhydrous salt • Calculate the amount of anhydrous salt in moles • Calculate the mass of the water lost • Calculate the amount in moles of water lost • Calculate the ratio of anhydrous salt to water and convert this to whole numbers • Write the formula of the hydrated compound
Water of crystallisation calculation • Find x in the formula MgSO4.xH2O if 5.00g of Magnesium Sulfate was dehydrated and 2.44g remained.