Question

what is the relationship between volatility and the vapor pressure of a solvent

Answer 1

The term volatile for a solvent is used to represent its tendency to vaporize i.e. more volatile a solvent, faster it will be vaporized and ultimately higher will be its vapor pressure at a given temperature. So, we can say that the volatility of a solvent is directly proportional to the vapor pressure of the solvent.

The relationship can be best understood as such,

• Take a pure volatile solvent in a beaker (of a closed container), and add some non-volatile solute particles into it to prepare a solution.
• Measure the boiling points in both cases.
• The volatile pure solvent will have a lower boiling point than that of the solution.
• This is because, when we add the non-volatile solute particles in the pure volatile solvent, the vapor pressure of the solvent (or the resulting solution) gets decreased due to more crowding of the non-volatile particles on the surface of the solvent. Due to the decrease in the vapor pressure, more heat is required to vaporize more particles so that the vapor pressure of the solution and the external atmospheric pressure become equal (i.e. the Boiling point).

The above example is also known as the elevation of the boiling point of a pure solvent due to the addition of non-volatile solute.

The reason why we connect the three terms namely Volatility, Vapor Pressure, and Boiling Point because they all are interrelated as below-

More volatile the solvent higher will be its vapor pressure, lower will be its boiling point!