Question

A handbook lists the value of the Henry's Law constant as 1.400 ✕ 10−3 mol L-1 atm-1 for methane, CH4, dissolved in water at 25°C. Calculate the mole fraction of methane in water at an methane partial pressure of 380. torr.

Answer 1

According to Henry's law, 'At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of gas in equilibrium with that liquid.'

The law can be expressed as,

p = K_H x X

where, p is the partial pressure of the gas, K_H is the Henry's law constant and X is the mole fraction.

Here, p = 380 torr = 0.5 atm, as 1 torr = 0.001315 atm

X = p / K_H

X = 0.5 / (1.400 x 10^-3)

X = 357

Therefore the mole fraction of methane in water will be 357.