4(ii)
A gas cylinder of capacity 40 dm3 is filled with gas X the mass of which is 20 g. When the same cylinder is filled with hydrogen gas at the same temperature and pressure the mass of hydrogen is 2 g. Find the relative molecular mass of the gas.
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Vapour density of gas =
$$\begin{aligned}\frac{\text{Wt. of certain volume of gas }}{\text {Wt. of same volume of H}_2} \\[0.5em] = \frac{20}{2} \\[0.5em] = 10 \text{ g}\end{aligned}$$
Molecular weight = 2 x Vapour density
= 2 x 10 = 20 g
Hence, relative molecular mass of gas is 20 g