# Class 11 Chemistry States of Matter: NCERT Solutions for Question 19

This page focuses on the detailed States of Matter question answers for Class 11 Chemistry States of Matter, addressing the question: 'A mixture of dihydrogen and dioxygen at one bar pressure contains 20% by weight of dihydrogen. Calculate the partial pressure of dihydrogen.'. The solution provides a thorough breakdown of the question, highlighting key concepts and approaches to arrive at the correct answer. This easy-to-understand explanation will help students develop better problem-solving skills, reinforcing their understanding of the chapter and aiding in exam preparation.
Question 19

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

Pressure of the gas mixture = 1 bar

Let us consider 100g of the mixture

So ,mass of hydrogen in the mixture  = 20 g

& mass of oxygen in the mixture = 80 g

Using the respective molar masses, we get

nH = 20/ 2  = 10 mol

. nO = 80 / 32 = 2.5 mol

Then, pH = XH x Ptotal

= (nH / nH + nO) x P total

= (10 / 10 + 2.5 ) x  1

= 0.8 bar

Hence, the partial pressure of dihydrogen is 0.8 bar.