Expression for Molar mass

Because the number of moles of a known mass $m$ of gas is $n = m/M$ (mass divided by molar mass), substituting this into the rearranged ideal gas equation $n = \frac{PV}{RT}$ gives $\frac{m}{M} = \frac{PV}{RT}$, which rearranges to $M = \frac{mRT}{PV}$. This means that, given the mass, pressure, volume and temperature of a gas sample, the ideal gas equation can be used directly to calculate the molar mass of an unknown gas or …