Question

A gas has a density of $3\text{g/L}$ at S.T.P. What is its molar mass?

• A. $67.2\text{g}$
• B. $40\text{g}$
• C. $20.4\text{g}$
• D. $10\text{g}$

Answer 1

The correct option is A $67.2\text{g}$

We know,
$PM=\rho RT$
where,
$M=$ Molar mass
$\rho =$ Density of gas
At STP;
$T=273\text{K},R=0.0821\frac{\text{atm-L}}{\text{K-mol}}$
$P=1\text{atm}$
$\therefore M=\frac{\rho RT}{P}=\frac{3\times 0.0821\times 273}{1}$
$\Rightarrow M=67.2\text{g}$