Vapour density of a compound is defined as the ratio of mass of a certain volume of gas to the mass of the same volume of hydrogen gas under conditions of temperature and pressure. Vapour density=Mass of certain of gas(22.4L)at STPMass of same volume ofH2gas(22.4L)at STP =Mw2 ...
for STP – standard temperature and pressure (273.15 K, 101.325 kPa) – the molar volume of an ideal gas is 22.413962x10-3 m3 mol-1 with standard uncertainty 0.000013 x 10-3 m3 mol-1.2