Question

A mixture of helium and argon contains 3 moles of He for every 2 moles of Ar. The partial pressure of argon in the mixture is:
A. two thirds the total pressure
B. one third the total pressure
C. three fifths the total pressure
D. two-fifths the total pressure

Answer 1

Hint: You should know that partial pressure is the mole fraction of the gas present in the mixture and the total pressure of the gaseous mixture is the sum of the partial pressure of each gas component.

Complete step by step solution:
First of all, let us have some knowledge on partial pressure.
Partial pressure is a measure of the concentration of a mixture of the individual components in a combination of gases. The total pressure applied by the combination is the sum of the partial pressures of the components in the mixture.
- The partial pressure exerted by any gas component in a mixture is directly proportional to the mole fraction (according to Dalton). So, the partial pressure of any gas component is the product of the mole fraction and total pressure.

In the question, it given that:
- A mixture of helium and argon contains $3$ moles of He for every $2$ moles of Ar.
So, helium contains three moles while argon has two moles and thus the total number of moles will be $2 + 3$.
Thus, the mole fraction of argon will be $=\dfrac{2}{2+3}$.
Let us consider total pressure as X.
So, the partial pressure of argon will be $=\dfrac{2}{2+3}.X=\dfrac{2}{5}X$.
Therefore, the partial pressure of argon will be two-fifth of the total pressure.
So, the correct answer is “Option D”.

Note: The total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the individual gases present in a mixture. It is important to note that the partial pressure is directly proportional to the mole fraction.