Question

Calculate the molecular mass of a gas if vapour density of the gas is $22$ .

Answer 1

Vapour density is the ratio of the mass of a volume of a gas, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure. Relative Molecular mass is defined as the ratio of the mass of one molecule of a substance to the mass $\dfrac{1}{{12th}}$ of a carbon atom. Molecular mass is known to be constant and is said to be independent of temperature and pressure.
Molecular mass $= 2 \times$ Vapour density

Complete answer:
Given: Vapour Density: $22$
To find: Molecular mass
Using the above formula,
Molecular mass $= 2 \times$ Vapour density
Substituting the given value in the formula we get,
Molecular mass $= 2 \times 22$
Molecular mass $= 44$
Therefore, the molecular mass of the gas will be $44$ .

Additional Information:
The molecular mass (molar mass) of any gas is said to be the mass of one particle of that gas multiplied by Avogadro's number. ( $6.022 \times {10^{23}}$ ). We can say that the speed of molecules in a gas is directly proportional to temperature and inversely proportional to molar mass of gas.

Note:
Vapour density is defined as the density of a gas with respect to the density hydrogen at same temperature and pressure. Therefore, the vapour density of an ideal gas is independent of temperature. The density of gases depends upon the temperature. When the temperature is higher, more molecules are spread out and lower is the density.