Gas Laws in Chemistry

Question

0.9811 g sample of an unknown gas occupies a 1.436 L glass container at a pressure of 0.540 atm and 29.6 ˚C. What is the molecular weight of the gas?

Answer 1

We are asked for the molecular weight (molar mass) of an unknown gas.

Molar mass = grams / mole. So, we need to know the grams and the moles and then it's easy to find molar mass.

We know the grams = 0.9811, so we now must find the moles. Use the ideal gas law

PV = nRT

P = pressure = 0.540 atm

V = volume = 1.436 L

n = moles = ?

R = gas constant = 0.0821 Latm / Kmol

T = temperature = 29.6ºC + 273 = 302.6K

Solve for n,

n = PV/RT

n = (0.540)(1.436) / (0.0821)(302.6)

n = 0.0312 mols

We now have what we need to find the molar mass

MOLAR MASS = g / moles = 0.9811 g / 0.0312 mols

MOLAR MASS = 31.4 g / mole