Question

A hydrate form of copper sulfate (CuSO4x H2O) is heated to drive off all the water. If we start with 9.31g of hydrated salt and have 5.95g of anhydrous CuSO4 after heating, find the number of water molecules associated with each CuSO4 formula unit.

Answer 1

Given:

Weight of hydrated salt = 9.31g

Weight of anhydrous CuSO₄ = 5.95g

So, weight of water = Weight of hydrated salt - Weight of anhydrous CuSO₄

Weight of water = 9.31g -5.95g = 3.36 g

Now determine the number of moles of both anhydrous CuSO₄ and water

(5.95 g CuSO₄) x [(1 mole CuSO₄)/(159.62 g CuSO₄)] = 0.0373 moles CuSO₄

(3.36 g H₂O) x [(1 mole H₂O)/(18.02 g H₂O)] = 0.1865 moles H₂O

Calculate the molar ratio to get the number of water molecules:

Molar ratio of H₂O/CuSO₄ = 0.1865/0.0373 = 5/1

Hydrate form of copper sulfate isCuSO_4.5 H₂O