Chemistry Gaseous State ( Not In Syllabus ) Ideal Gas Equation and Related Gas laws Single Correct MCQ
Published on: August 14, 2026

A mixture of nitrogen and water vapours is admitted to a flask which contains a solid drying agent. Immediately after admission, the pressure of the flask is 760 mm. After some hours the pressure reached a steady value of 745 mm.

A
Calculate the composition, in mol and per cent of original mixture.
B
If the experiment is done at 20ºC and the drying agent increases in weight by 0.15 g, what is the volume of the flask ? (The volume occupied by the drying agent may be ignored) ?

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Text Solution

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The correct answer is:
A

1.98% 10.156 litres

By Dalton's partial pressure

+ = 760 mm

From given data = 745 mm

So = 760 – 745 = 15 mm

% Mole of N 2 = % of pressure of N 2 = × 100 = 98.02

∴ Mole % of H 2 O = 100 – 98.02 = 1.98% Ans.

Increase weight of drying agent due to absorption of water (H 2 O).

Hence, Wt. of H 2 O = 0.15 g

∴ Mole of H 2 O =

Pressure of H 2 O( ) = 15 mm = atm

From gas equation PV = nRT

× V = × 0.0821 × (273 + 20)

V = 10.156 litres Ans.

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