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

Let the weight of dihydrogen be 20 g and the weight of dioxygen be 80 g.
Then, the number of moles of dihydrogen, $n_{H_2}=\frac{20}{2}=10$ moles and the number of moles
of dioxygen, $n_{O_2}=\frac{80}{32}=2.5$ moles
Given,
Total pressure of the mixture, $p_{total}=1$ bar
Then, partial pressure of dihydrogen,
$p_{H_2}=\frac{n_{H_2}}{n_{H_2}+n_{O_2}}\times P_{total}=\frac{10}{10+2.5}\times 1=0.8bar$
Hence, the partial pressure of dihydrogen is 0.8 bar