# Consider a steel container filled with 40.0 g of helium gas and 40.0 g of argon gas. What is the ratio of pressures that each gas exerts (helium:argon)? a) 1:1 b) 10:1 c) 1:10 d) 9:1

##### 1 Answer

The answer is **b) 10:1**.

When dealing with gas mixtures, it's important to remember that the partial pressures of the gases that make up the mixture depend on the number of moles each gas contributes to the total.

In your case, the total pressure in the container can be used to express the partial pressures of the two gases

**(1)**

**(2)**

where **mole fraction** of the helium gas and *total* number of moles present in the mixture.

So, use helium and argon's molar masses to determine how many moles you have in the mixture

This means you'll have a total number of moles equal to

The mole fractions for each of the two gases will be

Finally, divide equation **(1)** by equation **(2)** to get the pressure ratio you want