A 6.00 L tank at 14.7 C is filled with 4.19 g of chlorine pentafluoride gas and 10.1 g of sulfur hexafluoride gas. You can assume both gases behave as ideal gases under these conditions.

Question

Have to find the mole fraction, partial pressure and total pressure. I attempted this problem but it seems like I did something wrong, I'm not sure what though. I first found the mole fractions, then used the ideal gas law to find the pressure, and then multiplied the pressure with the mole fractions. I'm not sure what's wrong.

Answer 1

Let's first find moles of each gas and then mole fraction of each gas.

Chlorine pentafluoride = ClF₅ (molar mass = 130.4 g / mol

moles ClF₅ = 4.19 g x 1 mol / 130.4 g = 0.0321 mols ClF₅

Sulfur hexafluoride = SF₆ (molar mass = 146.1 g / mol)

moles SF₆ = 10.1 g x 1 mol / 146.1 g = 0.0691 mols SF₆

TOTAL MOLES = 0.0321 + 0.0691 = 0.1012 MOLES

Mole fraction ClF₅ = 0.0321 / 0.1012 = 0.317

Mole fraction SF₆ = 0.0691 / 0.1012 = 0.683

To find the total pressure and the partial pressure of each gas, you can do it by a couple of different approaches. You could use the moles of each gas and the ideal gas law to find pressure of each (partial pressure), then add them together to get total pressure. OR You could use the total moles in the ideal gas law to find the total pressure and then multiply that by the mol fraction for each gas to get the partial pressures. I'll use the 2nd approach.

PV = nRT (use total moles for n and solve for P)

P = pressure = ?

V = volume = 6.00 L

n = moles = 0.1012 mols

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 14.7C + 273.15 = 287.9K

Solving for P we have

P = nRT/V = (0.1012)(0.0821)(287.9) / 6.00

P = 0.399 atm = TOTAL PRESSURE

Partial pressure ClF₅ = 0.399 atm x 0.317 = 0.126 atm

Partial pressure SF₆ = 0.399 atm x 0.683 = 0.273 atm