Question

A $100\%$ pure sample of a divalent metal carbonate weighing $2g$ on complete thermal decomposition releases $448cc$ of carbon dioxide at STP. What is the equivalent mass of the metal?

Answer 1

Answer: 20

Divalent metal carbonate means $MC{O}_3$.
$\underset{\stackrel{1\mathrm{mole}}{2\mathrm{g}}}{\mathrm{MCO}{}_3}\text{->[}\mathrm{\Delta }\text{]}\mathrm{MO}+\underset{\stackrel{22400\mathrm{cc}}{448\mathrm{cc}}}{\mathrm{CO}{}_2}$
$448cc$ evolves from $2g$
$1cc$ evolves from $\frac{2}{448}g$
$22400cc$ will evolve from $\frac{2}{448}\times 22400g=100g$
i.e., $100g$ is the molecular weight of the carbonate.
Then $M$.Wt. of metal $=\underset{(\mathrm{wt}\cdot \mathrm{of}\mathrm{carbonate},\mathrm{CO}{}_3{}^{2-})}{100-(12+3\times 16)=40\mathrm{g}}$
Equivalent weight $=\frac{\text{Molecular weight}}{\text{Valency}}$
$=\frac{40}{2}=20$