Question

Density of a gas STP is $1.43g{L}^{-1}$ What is its molecular weight?

• A. $16$
• B. $32$
• C. $48$
• D. $64$

Answer 1

The correct option is B $32$

We know that $PV=nRT$

$PV=\frac{m}{M}RT$

$\Rightarrow PM=\frac{m}{V}RT$

$\Rightarrow PM=dRT$

At STP, $P=1atm$ $T=273K$ $R=0.0821litatm/mol-k$

$M=\frac{dRT}{P}=\frac{\left(1.43\right)\left(0.0821\right)\left(273\right)}{1}=32$ grams

$\therefore$ Molecular weight= $32grams$