Question

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

• A. $40$
• B. $20$
• C. $28$
• D. $12$
• E. $56$

Answer 1

The correct option is B $20$

Let the metal is $M$, so the formula of its carbonate is $MC{O}_3$.

Molar mass of $MC{O}_3=x+12+3\times 16$

$=(x+60)g/mol$

(Let atomic mass of $M$ is $x$.)

$\because 448cc\left(448mL\right)C{O}_2$ is produced from carbonate $=2g$.

$\therefore 22400ccC{O}_2$ will be obtained from carbonate $=\frac{2\times 22400}{448}=100g$

$\therefore 100=x+60$

$x=100-60=40g/mol$

Eq. wt. of metal $=\frac{40}{2}=20g{equiv}^{-1}$