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

Answer: (B)

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 $x$.)

$\underset{1mol}{MC{O}_3}\stackrel{\Delta }{\to }MO+\underset{1mol}{C{O}_2}$

$=22.4L=22400ML$

$\because 448$ cc $(448mL)C{O}_2$ 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 ${}^{-1}$