Question

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

Answer 1

We know that relationship of density $\left(d\right)$ of the substance at temperature $\left(T\right)$ is given as,
$d=MP/RT$
or, $P=dRT/M$
According to the question, if $M$ is the molar mass of the gaseous pxide, then
$2=dRT/M................\left(1\right)$
Also, for nitrogen, $5=dRT/\mathrm{28...........}\left(2\right)$ (given),
Dividing equation $\left(2\right)$ by $\left(1\right)$, we get
$5/2=M/28$
$M=5\ast 28/2=70g/mol$.
Hence, the molecular mass of the oxide is $70g/mol$.