When 30 g of crystalline calcium sulfate hydrate is calcined, 6.28 g of water is released.

When 30 g of crystalline calcium sulfate hydrate is calcined, 6.28 g of water is released. What is the formula of crystalline hydrate?

General formula of crystalline hydrate CaSO4 nH2O

CaSO4 nH2O = CaSO4 + nH2O

The number of moles of water n.

M (H2O) = 18g / mol.

M (CaSO4) = 136 g / mol.

Then М (CaSO4 nH2O) = 136 + 18n.

Let’s make a proportion.

Above the substances, we will sign the known data, below – the molecular weights.

CaSO4 nH2O = CaSO4 + nH2O

6.28 (136 + 18n) = 30 × 18n.

854 + 113.04 n = 540 n,

854 = 540 n – 113.04 n,

854 = 426.96 n,

n = 854: 426.96,

n = 2.

CaSO4 2H2O – calcium sulfate dihydrate.