**Question**

A balloon contains 0.1 moles of oxygen and 0.4 moles of nitrogen. If the balloon is at standard temperature and pressure, what is the partial pressure of the nitrogen?

**Solution**

Partial pressure is found by Dalton's Law

**P _{x} = P_{Total} ( n_{x} / n_{Total} )**

where

P_{x} = partial pressure of gas x

P_{Total} = total pressure of all gases

n_{x} = number of moles of gas x

n_{Total} = number of moles of all gases

**Step 1**

Find P_{Total}

Standard pressure is 1 atm

**Step 2**

Find n_{Total}

n_{Total} = n_{oxygen} + n_{nitrogen}

n_{Total} = 0.1 mol + 0.4 mol

n_{Total} = 0.5 mol

**Step 3**

Solve for P_{nitrogen}

P_{nitrogen} = P_{Total} ( n_{nitrogen} / n_{Total} )

P_{nitrogen} = 1 atm ( 0.4 mol / 0.5 mol )

P_{nitrogen} = 0.8 atm

**Answer**

The partial pressure of the nitrogen is 0.8 atm.