Question

A 100 % pure sample of a divalent metal carbonate weighing $2\,g$ on complete thermal decomposition releases $448\,cc$ 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 $MCO _{3}$.

Molar mass of $M CO _{3}=x+12+3 \times 16$

$=(x+60) g / mol$

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

$\underset{1 mol}{M CO _{3}} \overset{\Delta}{\to} M O + \underset{1 mol}{CO _{2}}$

$= 22.4 \,L= 22400 \,ML$

$\because 448$ cc $(448 \,mL ) CO _{2}$ is produced from carbonate $=2 g$

$\therefore 22400 cc CO _{2}$ will be obtained from carbonate

$ =\frac{2 \times 22400}{448}=100\,g $

$\therefore 100 =x+60$

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

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