For scuba dives below 150 ft, helium is often used to replace nitrogen in the scuba tank. If 15.2 g of He(g) and 30.6 g of O2(g) are added to a previously evacuated 5.00 L tank at 22° C, calculate the partial pressure of each gas present as well as the total pressure in the tank.

see explanation below

Explanation:

To do this exercise, we need to use the following expression:

P = nRT/V

This is the equation for an ideal gas. so, we have the temperature of 22 °C, R is the gas constant which is 0.082 L atm / mol K, V is the volume in this case, 5 L, and n is the moles, which we do not have, but we can calculate it.

For the case of the oxygen (AW = 16 g/mol):

n = 30.6 / 32 = 0.956 moles

For the case of helium (AW = 4 g/mol)_

n = 15.2 / 4 = 3.8 moles

Now that we have the moles, let's calculate the pressures:

P1 = 0.956 * 0.082 * 295 / 5

P1 = 4.63 atm

P2 = 3.8 * 0.082 * 295 / 5

P2 = 18.38 atm

Finally the total pressure:

Pt = 4.63 + 18.38

Pt = 23.01 atm