# At 18.0 Celsius and 765 torr, 2.29 dm^3 of a gas weigh 3.71 g. How to calculate the approximate molar mass, in g/mol, of the gas?

##### 1 Answer

The approximate molar mass of the gas is

In order to determine molar mass, which expresses the weight of 1 mole of gas, you need two things - the gas' mass, which you know to be **3.71 g**, and the number of moles of gas in that sample, which you must calculate.

Now, when dealing with gases always think ideal gas law equation,

*Notice that I've convertyed the pressure to atm, the volume to liters, and the temperature to K - all necessary if you want to use the 0.082 L atm/mol K value for R.*

Now that you know how many moles the sample contains, solve for the molar mass by