Which of the following change decrease the vapour pressure of water kept in a sealed vessel?
Which of the following change decrease the vapour pressure of water kept in a sealed vessel?
Decreasing the quantity of water
Adding salt to water
Decreasing the volume of the vessel to one-half
Keeping the temperature of water constant
Solution
When salt (non-volatile solute) is added to water kept in a sealed vessel, boiling point of the solution will be elevated or increased. So, vapour pressure of water (solution) will be decreased. Lowering of vapour pressure \(\left(\Delta p=p^{\circ}-p\right)\) is also proportional to mole fraction of the solute \(\left(\chi_B\right)\) present in the solution.
\(\Delta p \propto \chi_B\left[p^{\circ}=\right.\) vapour pressure of pure water \(p=\) vapour pressure of solution]