Question

200 g of a calcium carbonate sample decomposes on heating to give carbon dioxide and 80 g of calcium oxide. What will be the percentage purity of calcium carbonate in the sample?

Answer 1

Given: $CaC{O}_3\to CaO+C{O}_2$
1 mole of CaO is produced by the decomposition of 1 mole of $CaC{O}_3$
i.e. 56 g of CaO is produced by $\frac{100}{56}\times 80=142.85g$ of $CaC{O}_3$
$\%purity=\frac{\text{mass of pure compound in sample}}{\text{total mass of impure sample}}\times 100=\frac{142.85}{200}\times 100=71.43\%$

Hence, option (b) is correct.