Question

Define the terms:
(a) vapour density
(b) molar volume
(c) relative atomic mass
(d) Avogadro's number
(e) relative molecular mass

Answer 1

(a) Vapour density is defined as the density of vapours of a gas with respect to hydrogen at same temperature and pressure. It is the ratio of the masses of equal volumes of vapour or gas and the hydrogen gas at same temperature and pressure conditions.

Vapour density = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{volume}V\mathrm{of}\mathrm{the}\mathrm{gas}}{\mathrm{Mass}\mathrm{of}\mathrm{volume}V\mathrm{of}\mathrm{hydrogen}}$


(b) Molar volume is defined as the volume occupied by one mole of a substance at standard temperature and pressure (STP). Irrespective of gas taken, molar volume is always equal to 22.4 dm³ (litre).

(c) Relative atomic mass or atomic weight is defined as the ratio of the mass of the atom of an element to 1/12 times the mass of an atom of carbon-12. It is expressed in atomic mass unit (a.m.u.).
Relative atomic mass = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{an}\mathrm{atom}\mathrm{of}\mathrm{an}element}{{\displaystyle \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$12$}\right.}\mathrm{th}\mathrm{mass}\mathrm{of}\mathrm{one}\mathrm{C-12}atom}$

(d) Avogadro's number is defined as the number of atoms, ions or molecules present in one mole of a substance. It is denoted by N_A. Its value is equal to 6.023 $\times$ 10²³.

(e) Relative molecular mass of a molecule is the number of times the molecule is heavier than the 1/12th of the mass of a C-12 atom. It is calculated by adding the relative atomic masses of all the atoms present in a molecule. It is expressed as a whole number in atomic mass unit (a.m.u.).