Question

At $0^{\circ }C$ the density of gaseous oxide at 2 bar is same as that of nitrogen at 5 bar and $0^{\circ }C$. The molar mass of the oxide is (assuming ideal behaviour):

• A. $70g/mol$
• B. $140g/mol$
• C. $28g/mol$
• D. $60g/mol$

Answer 1

Answer: (A)

$70g/mol$

We know Density $\rho =\frac{M_{\rho }}{RT}⟶\left(1\right)$

For the given data if $M$ is the nolar mass of the gaseous oxide we have,

$\rho =\frac{M}{RT}.2$ or $2=\frac{\rho RT}{M}⟶\left(2\right)$

Also for nitrogen $5=\frac{\rho RT}{28}⟶\left(3\right)$

$\left(2\right)$ and $\left(3\right)\Rightarrow \frac{5}{2}=\frac{M}{28}$

or $M=\frac{5\times 28}{2}=70g/mol$