Question

Identify the law which is stated as “For any solutions, the partial vapour pressure of each volatile component in the solution is directly proportional to its mole fraction”.

• A. Dalton’s law
• B. Henry’s law
• C. Gay-Lussac’s law
• D. Raoult’s law

Hint:

Raoult’s law: \[ p_i = p_i^\circ x_i \] Henry’s law: \[ p = K_H x \] Raoult applies mainly to volatile liquid components, while Henry applies to gases dissolved in liquids.

Answer 1

The Correct Option is D

Understanding the Concept: Raoult’s law explains the relation between vapour pressure and mole fraction in ideal liquid solutions.
Step 1: Statement of Raoult’s law.
Raoult’s law states that: \[ p_i \propto x_i \] or \[ p_i = p_i^\circ x_i \] where:
\(p_i\) = partial vapour pressure of component
\(p_i^\circ\) = vapour pressure of pure component
\(x_i\) = mole fraction of component
Thus, the vapour pressure of each volatile component is directly proportional to its mole fraction.
Step 2: Comparing with other laws.

Dalton’s law deals with total pressure of gaseous mixtures.
Henry’s law relates pressure with solubility of gases in liquids.
Gay-Lussac’s law relates pressure and temperature of gases.
Only Raoult’s law matches the given definition.