5.6.1 Density and Molar Mass of a Gaseous Substance December 14, 2019 admin Ideal gas equation can be rearranged as follows: n/V = p/RT Replacing n by m/M we get m/MV = p/RT d/M = p/RT (where d is the density) On rearranging the above equation we get the relationship for calculating molar mass of a gas. M= (d RT)/p