# A 0.211 mol sample of an unknown gas contained in a 5.00 L flask is found to have a density of 2.50 g/L. The molecular weight of the unknown gas is g/mol.?

##### 1 Answer

#### Explanation:

The idea here is that the density of the gas tells you the mass of this gas that occupies exactly

In this case, you know that the gas had a density of

You also know that the total volume of the flask is equal to

#5.00 color(red)(cancel(color(black)("L"))) * "2.50 g"/(1color(red)(cancel(color(black)("L")))) = "12.5 g"#

Now, in order to find the **molar mass** of the gas, you need to find the mass of exactly **mole**. You know that this sample contains **moles** of gas and has a mass of **mole** will have a mass of

#1 color(red)(cancel(color(black)("mole gas"))) * "12.5 g"/(0.211 color(red)(cancel(color(black)("moles gas")))) = "59.24 g"#

Therefore, you can say that the molar mass of the gas is equal to

#color(darkgreen)(ul(color(black)("molar mass = 59.2 g mol"^(-1)))# This means that

#1# moleof this gas has a mass of#"59.2 g"# .

The answer is rounded to three **sig figs**.