Question

What happens to freezing point of benzene when small quantity of napthalene is added to benzene?

• A. Increases
• B. Remains unchanged
• C. First decreases and then increases
• D. Decreases

Answer 1

The Correct Option is D

This inquiry concerns the impact of introducing a small volume of naphthalene into benzene on its freezing point. This phenomenon is associated with colligative properties in chemistry, specifically the depression of freezing point. A comprehensive explanation follows:

Understanding Freezing Point Depression

The freezing point of a pure substance denotes the temperature at which it transitions from liquid to solid. When a solute is incorporated into a solvent, the solvent's freezing point is reduced. This effect is termed freezing point depression, a colligative property that is contingent on the quantity of solute particles present in the solvent, rather than the chemical nature of the solute.

Key Formula

The reduction in freezing point can be quantified using the following equation:

\(\Delta T_f = i \cdot K_f \cdot m\)

• \(\Delta T_f\) represents the alteration in freezing point.
• \(i\) is the van 't Hoff factor, indicating the number of particles the solute dissociates into.
• \(K_f\) is the cryoscopic constant specific to the solvent (in this instance, benzene).
• \(m\) denotes the molality of the solution.

Application to the Given Problem

Upon the addition of naphthalene to benzene:

• Naphthalene functions as the solute, and benzene serves as the solvent.
• The introduction of naphthalene particles into benzene leads to a depression in freezing point, as dictated by the aforementioned formula.

Conclusion

In accordance with the principle of freezing point depression, the incorporation of a small quantity of naphthalene into benzene results in a reduction of benzene's freezing point.

Correct Answer: Decreases