Question

The vapour density of a gas is 11.2. Find the volume occupied by 10g of the gas at STP.

Answer 1

Hint: STP in chemistry is the abbreviation for Standard Temperature and Pressure. STP most commonly is used when performing calculations on gases, such as gas density. The standard temperature is 273 K and the standard pressure is 1 atm pressure. This is the freezing point pure water at sea level atmospheric pressure. At STP, one mole of gas occupies 22.4L of molar volume.

Complete step by step solution:
First, let us know a few terms which will help us to solve the question!
Vapour Density: It’s the density of a vapour in relation to that of hydrogen. It is defined as the mass of a certain volume of a substance divided by the mass of the same volume of hydrogen. In simple words, it is the ratio of weight of a certain volume of gas compared to the weight of an equal volume of hydrogen.

Vapour density = Mass of n molecules of gas divided by mass of n molecules of hydrogen.

Let us see the relation between molecular mass and vapour density:
Relative molecular mass is the ratio of the mass of one electron of a substance to the 1amu. Vapour density is the ratio of the mass of a volume of a gas, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.

Let us now, apply these concepts and try to solve the question!

Vapour Density = half of Molecular mass

Therefore, Molecular mass of a gas= 22.4

So, Moles of the gas = $\dfrac {10} {22.4}$

Also, since 1 mole occupies 22.4 L at STP.

So, $\dfrac {10} {22.4}$ moles would occupy = $\dfrac{10} {22.4} \quad \times \quad 22.4\quad$ at STP.

Note: Vapour density concept is important, because it will indicate where the gas or vapours can generally be expected to be located at hazmat releases. The vapour density of ozone is 24.