Question

The Van't Hoff factor $I$ for a compound which undergoes dissociation in one solvent and association in other solvent is respectively :

• A. greater than one and greater than one
• B. less than one and greater than one
• C. less than one and less than one
• D. greater than one and less than one

Answer 1

The Correct Option is D

The Van't Hoff factor \(I\) is a measure of the effect of solutes on colligative properties, such as boiling point elevation and freezing point depression. It depends on whether the compound undergoes dissociation or association in a given solvent.

Let's break down the behavior of the Van't Hoff factor in the context of dissociation and association:

1. Dissociation:
   • When a compound dissociates in a solvent, it breaks into two or more smaller particles (ions or molecules).
   • This increases the number of particles in the solution, thereby increasing the Van't Hoff factor, \(I\) > 1.
2. Association:
   • When a compound associates in a solvent, it leads to the formation of a larger particle (fewer total particles in solution).
   • This decreases the number of particles in the solution, resulting in a reduction of the Van't Hoff factor, \(I\) < 1.

Given the options and the characteristics of dissociation and association:

• Greater than one and greater than one: This option doesn't apply because association leads to a Van't Hoff factor less than one.
• Less than one and greater than one: Incorrect as dissociation increases the Van't Hoff factor.
• Less than one and less than one: Incorrect as dissociation leads to \(I\) > 1.
• Greater than one and less than one: Correct. Dissociation yields \(I\) > 1 and association results in \(I\) < 1.

Thus, the correct answer is that the Van't Hoff factor for a compound is greater than one and less than one when it undergoes dissociation and association, respectively.