Question

At $0^{\circ }C$, the density of a certain oxide of a gas at $2$ bar is same as that of dinitrogen at $5$ bar. The molecular mass of the oxide is

• A. $10g$ mol ${}^{-1}$
• B. $20g$ mol ${}^{-1}$
• C. $50g$ mol ${}^{-1}$
• D. $70g$ mol ${}^{-1}$

Answer 1

Answer: (D)

$M_{oxide}=\frac{d_{\text{oxide}}RT}{P_{\text{oxide}}}....$(i)
$M_{N_2}=\frac{d_{N_2}RT}{P_{N_2}}....$(ii)
Dividing equation (1) by equation (2) gives
$\frac{M_{\text{oxide}}}{M_{N_2}}=\frac{d_{\text{oxide}}{P}_{N_2}}{d_{N_2}\times P_{oxide}}$
Given: $d_{oxide}=d_{N_2}\therefore M_{\text{oxide}}=\frac{5bar}{2bar}\times 28g$ mol${}^{-1}$
$M_{\text{oxide}}=70g$ mol ${}^{-1}$