Question

Two non-reactive monoatomic ideal gases have their atomic masses in the ratio $4: 5$. The ratio of their partial pressures when enclosed in a vessel kept at a constant temperature, is $1: 2$. The ratio of their densities is_________.

Answer 1

Using ideal gas equation: $P=\frac{\rho R T}{M}$
$\therefore \frac{P_{1}}{P_{2}}=\frac{\rho_{1}}{M_{1}} \times \frac{M_{2}}{\rho_{2}}$
$\therefore \frac{1}{2}=\frac{\rho_{1}}{\rho_{2}} \times \frac{5}{4}$
$\therefore \frac{\rho_{1}}{\rho_{2}}=\frac{2}{5}=0.4$