Question

Explain the relation between vapour density and molecular mass.

Short answer

Answer: Vapor density is directly proportional to the molecular mass of a substance, which means that as the molecular mass increases, the vapor density also increases, and vice versa. This relationship can be represented by the formula Vapor Density = (Molecular Mass of the Gas) / (Molecular Mass of Hydrogen).

Step-by-step solution

Definition of Vapor Density and Molecular Mass

Vapor density is defined as the mass of a certain volume of gas under specified conditions of temperature and pressure, expressed as a fraction of the mass of an equal volume of hydrogen under the same conditions. In other words, it is the ratio of the mass of a certain volume of gas to the mass of an equal volume of hydrogen at the same temperature and pressure. Molecular mass is the mass of a molecule of a substance, measured in atomic mass units (amu). It is calculated by adding up the atomic masses of all the atoms in a molecule.

Formula Relating Vapor Density and Molecular Mass

To relate vapor density and molecular mass, we use the following formula: Vapor Density = \(\frac{Molecular\:Mass\:of\:the\:Gas}{Molecular\:Mass\:of\:Hydrogen}\) where the molecular mass of hydrogen is 2 amu (because a hydrogen molecule is composed of two hydrogen atoms, each with a molecular mass of 1 amu).

Relation Between Vapor Density and Molecular Mass

From the formula derived above, we can see that the vapor density of a substance is directly proportional to its molecular mass. This means that as the molecular mass of a substance increases, its vapor density also increases, and vice versa. In other words, a gas with a higher molecular mass will have a higher vapor density compared to a gas with a lower molecular mass, when compared at the same temperature and pressure conditions. This relation can be helpful in determining the molecular mass of an unknown gas, and understanding its behavior under various conditions.