Problem 21 - A Complete Resource Book in Chemistry for JEE Main

Question

The vant Hoff factor 'i' accounts for (a) the extent of dissociation of solute (b) the extent of dissolution of solute (c) the degree of decomposition of solution (d) degree of solubilization of solute

Step-by-Step Solution

Answer

The van 't Hoff factor accounts for the extent of dissociation of solute.

Step 1: Define the van 't Hoff factor

The van 't Hoff factor \( i \) is used in colligative properties of solutions. It accounts for the effect of solute dissociation or association on the number of particles in a solution.

Step 2: Determine the correct context for 'i'

The van 't Hoff factor is particularly related to how many particles a solute yields in a solution. This relates to whether the solute dissociates into more ions or molecules upon dissolution.

Step 3: Identify dissociation relation

For a solute that dissociates, the van 't Hoff factor increases as one particle becomes multiple particles. Therefore, \( i \) is directly related to the extent of dissociation of the solute in the solution.

Key Concepts

Colligative Properties

Colligative properties are unique to solutions because they depend on the number, not the kind, of solute particles present. These properties are crucial in understanding phenomena like boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. They arise because the introduction of solute particles changes how the solvent behaves. Adding a solute usually decreases vapor pressure and increases boiling point. Likewise, the freezing point is lowered when a solute is present. This is because the solute particles disrupt the structure of the liquid, making phase changes less favorable. Colligative properties are only affected by the number of particles, regardless of whether those particles are molecules, ions, or a mix of both. This highlights the importance of counting particles in solutions. The impact of these properties is described by the van 't Hoff factor, which helps quantify the effect of solute dissociation on these properties.

Solute Dissociation

When a solute dissolves in a solvent, it may dissociate into two or more individual ions or molecules. This process of solute dissociation is crucial for determining how many particles form in a solution. Certain solutes, such as salts, dissociate completely into ions, such as NaCl in water, which separates into Na⁺ and Cl⁻ ions. The extent of dissociation influences how the solution behaves in terms of colligative properties. A solute that dissociates into more particles increases the effective number of solute particles, impacting properties like boiling point elevation or freezing point depression. The van 't Hoff factor, designated as "i," measures this change in particle number due to dissociation or association. For example, a salt that fully dissociates into two ions might have a van 't Hoff factor close to two. However, real-life scenarios often involve partial dissociation, requiring careful calculation of "i" based on the actual number of particles formed.

Number of Particles in Solution

Understanding the number of particles in a solution is fundamental to predicting and explaining colligative properties. The more particles present, the more significant the effect on properties such as boiling point and freezing point. The total number of particles can vary based on whether the solute dissociates or not. When dealing with solutions, it's important to account for dissociation which can increase the number of particles dramatically. For instance, when a solute like calcium chloride (CaCl₂) dissociates, it forms three ions: one Ca²⁺ and two Cl⁻. This indicates a higher van 't Hoff factor, approximating three, meaning more particles in the solution than the initial solute particles would suggest. Thus, understanding the dissociation and the number of particles generated is key to solving problems involving colligative properties. It provides insights into how solutions will behave under different conditions and helps in making predictions about their physical properties.