Question

Find the value of x in a formula for hydrated calcium salt, CaSO4.xH2O, when 1.600 g of it on heating produce 1.767 g of anhydrous calcium sulfate, CaSO4.

Answer 1

I'm sure that you mean to say 1.767 g of CaSO₄.2H₂O on heating produces 1.6 g of CaSO₄ because the molar mass of CaSO₄.xH₂O is higher than that of CaSO₄.

Outline: When 'n' no. of moles of CaSO₄.2H₂O on heating produces the same (n) no. of moles of CaSO₄.

Now, no. of moles of CaSO₄ = 1.6 g/136.134 gmol^-1 = 0.01175 mol

And the no. of moles of CaSO₄.xH₂O should be 0.01175 mol = 1.767 g/0.01175 mol = 150.343 gmol^-1 ~ 154.149, which is the molar mass of CaSO₄.1H₂O

Hence, x = 1