Question

At 0°C, the density of a certain oxide of a gas at 2 bar 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 (d) of the substance at temperature (T) is given as
d = MP/RT
or, P = d RT/ M
According to the question, if M is the molar mass of the gaseous oxide, then
2 = dRT/M …(1)
Also for nitrogen, 5 = dRT/28 …(2) (Given)
Dividing equation (2) by (1), we get
5/2 = M/28
M = 5 × 28/2 = 70 g/mol
Hence, the molecular mass of the oxide is 70 g/mol.