Gypsum is hydrated calcium sulfate. a 4.89 g sample of this hydrate was heated. after the water was removed, 3.87 g anhydrous calcium sulfate remained. determine the formula of this hydrate and name the compound.

Answer is: c alcium sulfate dihydrate (CaSO₄ · 2H₂O)

m (CaSO₄ · xH₂O) = 4,89 g.

m (CaSO₄) = 3,87 g.

n (CaSO₄) = m (CaSO₄) : M (CaSO₄)

n (CaSO₄) = 3,87 g : 136 g/mol = 0,0285 mol.

m (H₂O) = m (CaSO₄ · xH₂O) - m (CaSO₄).

m (H₂O) = 4,89 g - 3,87 g

m (H₂O) = 1,02 g.

n (H₂O) = m (H₂O) : M (H₂O)

n (H₂O) = 1,02 g : 18 g/mol

n (H₂O) = 0,057 mol.

n (CaSO₄) : n (H₂O) = 0,0285 mol : 0,057

n (CaSO₄) : n (H₂O) = 1 : 2