20.0 g of a magnesium carbonate sample decomposes on heating to give CO₂ and 8.0 g magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample?

Options

(a) 75
(b) 96
(c) 60
(d) 84

Correct Answer:

84

Explanation:

MgCO₃ -> MgO + CO₂
84 g of MgCO₃ form 40 g of MgO
20g of MgCO₃ form (40 * 20) / 84 g of MgO
= 9.52 g of MgO
Since 8 g of MgO is formed, purity = (8 / 9.52) *100 = 84%