What is the molar mass of a gas that has a density of 1.18g/L at 25°C and 1 atm?
We are going to solve this by first figuring out what the volume of one mole of a gas is at
Let us start with the Ideal Gas Law: PV=nRT.
For 1 mole of a gas, n=1. You are at (
R = 0.082057 liter-atm/mol-K.
So, solving PV=nRT for V, V=nRT/P = 24.453 liters.
So now we know that we need 24.453 liters of gas to get one mole. That much gas will weigh:
24.453 liters *1.18 g/liter = 28.854 grams per mole.
Adjusting to 3 significant figures: 28.9 grams per mole.
The key was figuring out how many liters of gas we needed to make one mole, and we got that from the Ideal gas Law.