Question

Which of the following gases is heavier than air?
(a) nitrogen
(b) carbon monoxide
(c) ammonia
(d) Sulphur dioxide

Answer 1

Hint: For an ideal gas, the density is just the molecular weight of the gas, divided by the volume of a given number of molecules. Since a given number of molecules always takes up the same volume for a gas, the higher the molecular weight, the heavier the gas is or the heavier the density.

Complete step by step answer:
- We have been asked about the gas which is heavier than air,
- So, for that we need to calculate the density of the gas,
- The density of a gas is roughly proportional to its molecular weight. Air has an average molecular weight of about 29 g/mol, so any gas with a molecular weight heavier than this will be denser than air.
Thus, if we take an example of ammonia and chlorine,
- It is lighter than air because its molar mass (17.03 g/mol) is less than 28.97 g/mol, the average molar mass of air. On the other hand, chlorine is much heavier than air because its molar mass (70.9 g/mol) is much greater than that of air that is (28.97 g/mol).
- Now, vapour density for Sulphur dioxide is 32, for nitrogen is 14, carbon monoxide is 14 and ammonia is 8.5.
- So, in comparison we can say that Sulphur dioxide has a density more than that of air that is 28.97 g/mol.
so, we can say that Sulphur dioxide is heavier than air.
The correct answer is option “D” .

Note: When calculating the weight of dry air molar mass is considered and calculated other than density or vapor density. Also, while calculating the density of air use the formula: the mass per unit volume of earth’s atmosphere.