Question

The masses of equal volumes of a gas and hydrogen are 25.6 g of 0.8 g respectively under same conditions of temperature and pressure. Find the molecular mass of the gas.

Answer 1

It is known that 22.4 L of any gas at STP weigh equal to the molecular mass of the gas expressed in grams.
Thus, 22.4 L of hydrogen will weigh 2 g.
Let x L of hydrogen weighs 0.8 g
therefore x = $$\begin{gathered} \frac{0.8\times 22.4}{2} \\ =8.96 \end{gathered}$$
So 8.96 L of H₂ gas will weigh 0.8 g
Since, volume of two gases are equal, so 8.96 L of other gas will weigh 25.6 g
Thus 22.4 L of gas will weigh y grams
y = $\frac{22.4\times 25.6}{8.96}$
= 64 g
Hence molecular mass of gas is 64 g