Question

How do you calculate the vapour pressure of a solution?

Answer 1

Hint We can calculate the vapour pressure of a solution by using Raoult’s law. As this law basically shows the relation between the vapour pressure and the mole fraction of the solute.

Complete Step by step solution:
- As we know that Raoult’s law states that for an ideal solution, the partial vapour pressure of a component in that solution is equal to the mole fraction of that component multiplied by its vapour pressure when pure.
- If we are dealing with a solution that is having a volatile solute than we can write the vapour pressure of that solution as:
  ${{P}_{solution}}={{x}_{solvent}}\times P_{solvent}^{0}+{{x}_{solute}}\times P_{solute}^{0}$
- Where,
= the vapour pressure of the pure solute
${{x}_{solute}}$= mole fraction of the solute
- If we are dealing with a solution that is having a non-volatile solute, that is a solute which basically doesn't have tendency to form vapour at the temperature of the solution, then we can write the vapour pressure of that solution as;
${{P}_{solution}}={{x}_{solvent}}\times P_{solvent}^{0}$
- Where,
$P_{solvent}^{0}$= the vapour pressure of the pure solvent
${{P}_{solution}}$= the vapour pressure of the solution
 ${{x}_{solvent}}$ =mole fraction of the solvent
- Hence, we can calculate the vapour pressure of a solution by using these formulas.

Note:
- As we know that temperature is the major factor that affects the vapour pressure. It is found that as the temperature of a solid or a liquid increases, the vapour pressure also increases and vice versa.