Question

Partial pressure of a solution component is directly proportional to its mole fraction. This is known as:
(A) Henry’s law
(B) Raoult’s law
(C) Distribution law
(D) Ostwald’s dilution law

Answer 1

Hint: To answer this question we should know the definitions of the various laws. Mole fraction is a unit less quantity. Partial pressures are used to indicate the vapour pressures of the constituents of a mixture.

Complete step by step solution:
Let’s look at the definitions of the laws mentioned in the question.

Henry’s law: It states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas at a constant temperature. So, option (A) is not the answer.

Raoult’s law: It states that the partial pressure of each component of an ideal mixture of liquids is proportional to the mole fraction of the component in the mixture. The vapour pressure of the components is taken. So, option (B) is the correct answer.

Distribution law: It is also known as Nernst’s distribution law. According to this law a solute distributes itself between two immiscible solvents only in a particular ratio at a constant temperature. So, option (C) is also incorrect.

Ostwald’s dilution law: According to this law, at infinite dilution the degree of ionization of a weak electrolyte is inversely proportional to the square root of concentration and directly proportional to the square root of the dilution. So, option (D) is also incorrect.

Hence, the answer for the given question is option (B).

Note: Raoult’s law is valid only for ideal solutions. The definitions of Henry's law can be confused with Raoult’s law. Raoult’s law is a special case of Henry’s law when the Henry’s constant becomes equal to the vapour pressure of the pure component.