Question

A hydrated form of copper sulfate (CuSO4·x H2O) is heated to drive off all the water. If we start with 8.79 g of hydrated salt and have 6.57 g of anhydrous CuSO4 after heating, find the number of water molecules associated with each CuSO4 formula unit.

Answer 1

Answer:

3 water molecules

Explanation:

The molar ratio between CuSO₄ and H₂O needs to be calculated.

The mass of water that was removed by heating is calculated, then converted to moles. The molecular weight of water is 18.02g/mol.

(8.97 g - 6.57 g) = 2.22 g H₂O

(2.22 g)/(18.02g/mol) = 0.1232 mol H₂O

The moles of anhydrous copper sulfate are calculated. The molecular weight is 159.609 g/mol

(6.57 g)/(159.609 g/mol) = 0.04116 mol CuSO₄

Now the molar ratio between CuSO₄ and H₂O can be calculated:

0.1232 mol H₂O ÷ 0.04116 mol CuSO₄ = 3 H₂O / CuSO₄