Chemistry - Ideal Gas Question with Solution | TestHub
A barometer tube contains a mixture of air and saturated water vapour in the space above the mercury column. It reads 68 cm when the actual atmospheric pressure is 76 cm of Hg. The saturation vapour pressure at room temperature is 2.0 cm of Hg. The tube is now lowered in the reservoir till the space above the mercury column is reduced to half of its original volume. The reading of the barometer (in cm) is (Assume that the temperature remains constant.)
Answer:
Solution:
Initially trapped-gas pressure = 76 - 68 = 8 cm Hg, of which saturated water vapour contributes 2.0 cm; dry air part = 6.0 cm at volume V₀.
On halving the space the vapour stays saturated at 2.0 cm (excess condenses); air obeys Boyle: pₐir = 6.0 x V₀/(V₀/2) = 12 cm Hg.
Total trapped pressure = 12 + 2 = 14 cm Hg.
Barometer reading = 76 - 14 = 62 cm ⇒ 0062.
