Question

At STP, 5.6 litre of a gas weighs 60 g. The vapour density of gas is:
Options
A.60
B.120
C.30
D.240

Answer 1

The density of a vapour in comparison to hydrogen is known as the vapour density. It can be calculated by dividing the mass of a given volume of a matter by the mass of the same volume of hydrogen.

Complete answer:
The density of a vapour in comparison to hydrogen is known as vapour density. It can be calculated by dividing the mass of a given volume of a matter by the mass of the same volume of hydrogen.
At STP, 1 mole of gas has a volume of 22.4 L
Then number of moles in 5.6 L gas will be = $\dfrac{{5.6}}{{22.4}}$= 0.25 moles
If 0.25 moles of gas weighs 60 g
Then 1 mole of gas weighs = $\dfrac{{60}}{{0.250}}$ = 240g
The molar mass of a chemical compound is known as the mass of a sample divided by the amount of material in the sample, measured in moles, in chemistry.
Molar mass = 240g
Molar mass = 2 × Vapour density
240 = 2 × V.D
Vapour Density = 120

Hence, B is the answer.

Note:
The density of a vapour in comparison to hydrogen is known as the vapour density. It can be calculated by dividing the mass of a given volume of a matter by the mass of the same volume of hydrogen.
The molar mass of a chemical compound is known as the mass of a sample divided by the amount of material in the sample, measured in moles, in chemistry.