Question

A mixture of dihydrogen and dioxygen at one bar pressure contains 20% by weight of dihydrogen. Calculate the partial pressure of dihydrogen.

Answer 1

In 100 g of mixture, the mass of hydrogen and oxygen will be 20 and 80 g respectively.
The number of moles of hydrogen are $n=\frac{20}{2}=10$.
The number of moles of oxygen are $n^{\prime }=\frac{80}{32}=2.5$.
The mole fraction of hydrogen is $\frac{10}{10+2.5}=0.8$.
Partial pressure of hydrogen is $0.8\times P=0.8\times 1=0.8bar$.