# whats 'vapour density' of a gas????

Grade:12

## 2 Answers

Prudhvi teja
83 Points
13 years ago

Dear samidha

Vapour density is the density of a vapour in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen.

vapour density = mass of n molecules of gas / mass of n molecules of hydrogen

(By definition, the molar mass of a gas is the ratio of the mass of one molecule of gas to that of an hydrogen atom under similar conditions.)

Therefore:

vapour density = molar mass of gas / molar mass of H2

vapour density = molar mass of gas / 2

vapour density = ½ × molar mass

(and thus: molar mass = 2 × vapour density)

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Srinivas Rao
11 Points
13 years ago

Vapour density is a relative scale of measurement that tells us how many times a given gas is heavier than Hydrogen, when all measurements are made at identical conditions.

So, vapour density = Mass of the given gas / Mass of the same volume of H2

As the Molecular weight of hydrogen is 2 amu,

V.D = Molecular Wt of the given gas / 2

2 x V.D = molecular wt of the given gas.

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