Question

Assertion: When a non-volatile solute is added to pure water, the vapor pressure of the water will decrease.
Reason: All solutes dissociate into positive and negative ions.

• A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion
• B. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
• C. Assertion is true but Reason is false
• D. Assertion is false but Reason is true
• E. Both Assertion and Reason are false

Answer 1

Answer: (C)

Assertion is true but Reason is false

Vapor pressure is a measurement of the likelihood of the molecules of a pure solvent to change from the liquid to the vapor phase. If we add a non volatile solute to solvent such as water, we decrease the tendency for water molecules to evaporate into the gas phase. In essence, the solute particles obstruct or reduce the likelihood of evaporation.

As a result, fewer molecules change from the liquid to the gas phase, thus reducing the vapor pressure. so Assertion is true.

All solutes do not dissociate into positive and negative ions, so Reason is false.