Question

Consider the given plots of vapor pressure (VP) vs temperature (T/K). Which amongst the following options is the correct graphical representation showing \( \Delta T_f \) depression in the freezing point of solvent in a solution?

• A.
• B.
• C.
• D.

Hint:

In freezing point depression, the presence of solute decreases the vapor pressure of the solvent, resulting in a lower freezing point. This is a colligative property that depends on the amount of solute, not its identity.

Answer 1

The Correct Option is C

To understand the graphical representation for the depression in the freezing point of a solvent in the solution, it's essential to understand the concept of colligative properties. Depresssion in the freezing point is one such colligative property, exhibiting the effect of solute addition on the solvent properties. The vapor pressure of the solvent decreases upon solute addition, resulting in a lower freezing point. 

1. Concept Explanation:
   • When a non-volatile solute is added to a solvent, the solute particles disrupt the regular crystal structure of the solvent, lowering its freezing point compared to the pure solvent. This phenomenon is known as freezing point depression (\(\Delta T_f\)).
   • In terms of vapor pressure, the presence of a solute decreases the vapor pressure of the solvent. At the freezing point, the solid and liquid phases are in equilibrium.
   • The change in the vapor pressure at different temperatures will show differences from the ideal conditions, causing a shift in the freezing point.
2. Graphical Representation:
   • We need to find the graph showing a drop in the freezing point due to the addition of solute. Look for a graph where the vapor pressure curve intersects at a lower temperature for the solution compared to the pure solvent.
3. Analyzing the Options:
   • The correct graph will show the solution's vapor pressure as being lower than that of the pure solvent, such that the intersection with the solid line occurs at a lower temperature, aligning with the decrease in freezing point (\(\Delta T_f\)).
   • Let's identify such a graph. Based on the provided options, the correct representation is:
4. Conclusion:
   • This graph shows how the vapor pressure curve for the solution intersects the line representing the solid state at a lower temperature when compared to the pure solvent. Thus, it correctly depicts the depression in freezing point (\(\Delta T_f\)) due to the addition of a solute.

Answer 2

Freezing point depression occurs when a solute is added to a solvent, lowering its freezing point.
The correct graph shows the vapor pressure curve of the solution below that of the pure solvent, with the freezing point of the solution occurring at a lower temperature.
The correct representation is \( \text{Option (3)} \), where the freezing point depression (\( \Delta T_f \)) is clearly shown, with the solution curve below the solvent curve.
Thus, the correct answer is: \( \boxed{(3)} \).