Question

An impure sample of $5gCaC{O}_3$ on thermal decomposition gives $30$g of impure $CaO$ find the amount of pure sample.

Answer 1

$CaC{O}_3\to CaO+C{O}_2$

$100$ $56$ $44$

Molar mass of $CaC{O}_3=40+12+48=100g$

$100g$ gives $44g$ of $C{O}_2$ & $56g$ of $CaO$

$CaO\to 3g$ is obtained from $\frac{3\times 100}{56}$

$=5.35g$ of $CaC{O}_3$

Mass of impurities= $5.35-5.0=0.35$

Percentage of impurities= $\frac{0.35}{5}\times 100=7$%