Question

40 gm of a magnesium carbonate sample decomposes on heating to give carbon dioxide and 16 gm magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample.

• A. 60%
• B. 84%
• C. 75%
• D. 96%

Answer 1

The correct option is B 84%

$MgC{O}_3\to MgO+C{O}_2$

1 mole of $MgO$ is formed from 1 mole of $MgC{O}_3$

40 g of $MgO$ is formed from 84 g of $MgC{O}_3$

Hence mass of $MgC{O}_3$ present in the sample $=\frac{16}{40}\times 84=\frac{2}{5}\times 84$
$\text{percentage of purity}=\frac{2\times 84}{40\times 5}\times 100=84\%$