Question

Plaster of paris is calcium sulfate monohydrate, (CaSO4)2.H2O. If you heat 20.00g of hydrate and drive off the water, what is the mass of the anhydrous salt remaining? Show your work.

Answer 1

Plaster of paris is calcium sulfate monohydrate = (CaSO4)2.H2O

mass of hydrate heated = 20.0 g

molar mass = 290 g/mol

% of water = (18/290) x 100

                  = 6.2% by weight

so mass of water lost will be = 0.062 x 20

                                             = 1.24 g

so total mass of unhydrates remained = 20-1.24

mass of unhydrates remained = 18.76 g