Question

11. A 4.175 gram sample of a certain hydrate of copper (II) sulfate, CuSO,• xH,O, is heated until all
the water is driven off. The resulting anhydrous compound weighs 3.120 grams. What is the
formula of the hydrate?

Answer 1

The  formula of the hydrate = CuSO₄• 3H₂O

Further explanation

Given

4.175 grams sample CuSO₄• xH₂O

3.120 grams anhydrous compound CuSO₄

Required

The formula

Solution

mass of H₂O driven off :

= 4.175 - 3.12

= 1.055 g

MW CuSO₄ = 159.5 g/mol

MW H₂O = 18 g/mol

mol ratio of CuSO₄ : H₂O :

= 3.12/159.5 : 1.055/18

= 0.01956 : 0.05861

= 1 : 3

Answer 2

Based on the data provided, the formula of the hydrated salt is CuSO4.3H20

What is the formula of the hydrate?

The formula of the hydrate is determined from the mole ratio of the anhydrous saltand water.

Mass of water = 4.175 - 3.120

mass of water = 1.055 g

Mole ratio= mass/molar mass

molar mass of CuSO4 = 160 g/mol

molar mass of H2O = 18 g/mol

CuSO4 = 3.120/160 = 0.0195

H2O = 1.055/18 = 0.0586

CuSO4 = 0.0195/0.0195 = 1

H2O = 0.0586/0.0195 = 3

Therefore, the formula of the hydrated salt is CuSO4.3H20

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