12 grams of a calcium carbonate sample with non volatile impurities, on complete decomposition left 7.6 grams of residue. What is the percentage of impurities in the sample ?

Mass of sample = 12 gms

Mass of residue = 7.68 gms (includes impurities)

$\therefore$ Mass of $C{O}_2$ released = 12-7.6 = 4.4 gms

$44gmC{O}_2\equiv 100gmCaC{O}_3$

$\therefore 4.4gmC{O}_2\equiv 10gmCaC{O}_3$

$\therefore$ Mass of impurities = 12-10=2 gms.

$\therefore$ % impurities $=\frac{2}{12}\times 100= 16.6 \%$