A large flask with a volume of 936 mL has a mass of 134.66 g. Later filled to a pressure of 0.967 atm at 31 °C with unknown gas and given a new mass of 136.34 g. What is the molar mass of this gas?

Question

A large flask with a volume of 936 mL is evacuated and found to have a mass of 134.66 g. It is then filled to a pressure of 0.967 atm at 31 °C with a gas of unknown molar mass and then reweighed to give a new mass of 136.34 g. What is the molar mass of this gas?

Answer 1

To solve this problem, we will need to use the ideal gas law: PV = nRT

P = 0.967 atm

V = 0.936 L

n = ?

R = 0.082 Latm/molK

T = 304 K

We wil solve for n, the number of moles, then convert to grams/mole (molar mass) using the mass of the gas, which we get from total mass - initial mass.

First, lets solve for n:

n = (PV) / (RT)

n = (0.967 x 0.936) / (0.082 x 304)

n = 0.0363 mol

Now, lets find the mass of the gas. This would be the new mass minus the mass of the flask.

mass = 136.34 - 134.66

mass = 1.68 grams

Molar mass is grams per mole, so we will divide this mass by the number of moles.

Molar mass = 1.68 grams / 0.0363 mol

Molar mass = 46.26 g/mol

Hope that helps!