Question

2.55 g of an unknown gas at 43 °C and 1.00 atm is stored in a 2.25-L flask.

What is the density of the gas?

What is the molar mass of the gas?

Answer 1

Density = mass/volume

Density of the gas in g/L = 2.55g/2.25L = 1.13g/L

Density of the gas in g/ml = (2.55 g) / (2250 ml) = 0.00113 g/ml = 1.13 x 10^-3 g/ml

Use the ideal gas equation to calculate moles of gas

PV = nRT

Where

P = 1.00 atm

V =2.25-L

T = 43 °C +273 = 316 K

R = gas constant = 0.08205746 L atm/K mol

n = PV/RT

n = ((1.00 atm) (2.25-L)) / ((0.08206 L atm/K mol) x (316 K)) = 0.08676 mol

Now, divide mass by moles to get molar mass of gas

Molar mass of gas = 2.55 g/0.087 mol = 29.31 g/mol