JAMB Chemistry 1988 Question 15

Question 15

Mole Concept and Stoichiometry

1.34 g of hydrated sodium tetraoxosulphate (VI) was heated to give an anhydrous salt weighing 0.71 g. The formula of the hydrated salt is [Na = 23, S = 32, O = 16, H = 1]

A.Na₂SO₄.7H₂O
B.Na₂SO₄.3H₂O
C.Na₂SO₄.2H₂O
D.Na₂SO₄.H₂O

Show the answer and explanation

Answer: A (Na₂SO₄.7H₂O)

Explanation

Anhydrous Na₂SO₄: 0.71/142 = 0.005 mol. Water lost: 0.63 g = 0.035 mol. Ratio 0.035/0.005 = 7, so Na₂SO₄.7H₂O.