Question

When determining the pressure of dry hydrogen gas, explain how the measured atmospheric pressure is corrected for the following:

a. the presence of water vapor

b. a level of liquid in the tube higher than that in the beaker

Answer 1

a) the presence of water vapour is corrected by noting the vapour pressure of water vapour at the given temperature. (these are measured and standard values)

The vapour pressure is substracted from the pressure measured during experiment

total Pressure = Pressure of hydrogen + vapour pressure

so pressure of hydrogen = Total pressure - vapour pressure

b) a level of liquid in the tube higher than that in the beaker : Due to this the pressure of gas inside the tube used will be less as compared to the atomospheric pressure.

To overcome the same problem we will convert the height of the solution column in terms of height of mercury column ( mm Hg)

Remebmer : mmHg is a unit of pressure

so during calculation we will substract this as pressure from the actual pressure noted.