The partial vapour pressure of an electrolyte at the following concentrations, decreases in the order
(A) 0.5 M
(B) 0.1 M
(C) 0.05 M
(D) 0.001 M
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C), (D)
The partial vapour pressure of a component of a solution depends on how much of it is present. By Raoult’s law for a volatile component (or Henry’s law for a dissolved gas such as HCl), the partial vapour pressure is directly proportional to its mole fraction in the solution:
\( \displaystyle p_{\text{solute}} = p^\circ_{\text{solute}}\,x_{\text{solute}} \quad \text{or} \quad p_{\text{solute}} = K_H\,x_{\text{solute}} \)
For dilute solutions the mole fraction of the solute is proportional to its molarity. So the partial vapour pressure of the electrolyte is highest in the most concentrated solution and falls as the concentration falls:
\( \displaystyle 0.5\,\mathrm{M} \gt 0.1\,\mathrm{M} \gt 0.05\,\mathrm{M} \gt 0.001\,\mathrm{M} \)