Calculate the formula of the hydrated crystal?

Question

A 4 g sample of the hydrated crystal Ba(OH)2• χH2O is heated until all the water is removed. The remaining solid weighs 2.17 g. Calculate the formula of the hydrated crystal

Answer 1

4 g-2.17 g=1.83 g H2O

Molar mass of Ba(OH)2=171.3 g/mol

171.3/2.17=78.94

78.94*1.83=144.5 g H2O

144.5 g H2O x 1 mol H2O/18 g H2O=8.0 mol H2O

Hydrate formula: Ba(OH)2•8H2O