A mixture of He, Ne and Ar has a pressure of 7.85 atm. If the Ne has a mole fraction of 0.47 and Ar has a mole fraction of 0.23, what is the pressure of He?

2.355atm

Explanation:

To get the pressure of helium, we need to get the mole fraction of helium.

The total mole fraction for any mixture of gases equals 1. Hence to get the mole fraction of the helium, we simply subtract the addition of the mole fractions of neon and argon from 1.

This means - 1 - 0.47 - 0.23 = 0.3

Now, to get the pressure of the helium gas, we simply multiply the total pressure by 0.3. This is 0.3 * 7.85 = 2.355 atm