# Question b7884

Jan 28, 2015

The relative molecular mass of the gas is $\text{39.2 g/mol}$.

A very important thing happens at STP with ideal gases: 1 mole of any ideal gas occupies $\text{22.4 L}$ - the molar volume of a gas. Since density is defined as mass per unit volume, you can automatically find the mass of 1 mole of gas (notice that I've converted $\text{1 L}$ to 1 ${\text{dm}}^{3}$)

rho = m/V => m = rho * V_("molar") = "1.750 g/dm"^3 * "22.4 dm"^3#

$m = \text{39.2 g}$

Therefore, the gas' molar mass is

$\text{molar mass" = ("39.2 g")/("1 mole") = "39.2 g/mol}$

This is pretty close to $\text{Ar}$'s molar mass, so that could be the identity of the gas.