Chemistry · Ch 5 — States of Matter

Density and Molar Mass of a Gaseous Substance

5.6.1

Starting from the ideal gas equation and rearranging for the molar amount per volume:

\frac{n}{V} = \frac{p}{RT}

Replacing $n$ with $\dfrac{m}{M}$ (mass over molar mass):

\frac{m}{MV} = \frac{p}{RT}

Since density $d = \dfrac{m}{V}$ , this becomes:

\frac{d}{M} = \frac{p}{RT}

Rearranging one more time gives a direct route to a gas's molar mass from an experimentally measured density:

$M = \frac{dRT}{p}$ …