Question

The values of colligative properties of colloidal solution are of small order in comparison to those shown by true solutions of same concentration because of colloidal particles (a) Remain suspended in the dispersion medium (b) Form lyophilic colloids (c) Are comparatively less in number (d) Exhibit enormous surface area

Short answer

Colloidal particles are less in number, resulting in smaller colligative effects.

Step-by-step solution

Understanding Colligative Properties

Colligative properties are physical properties of solutions that depend on the number of solute particles, but not on their identity. These include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Interpretation of the Question

The exercise asks why the colligative properties of colloidal solutions are much smaller compared to true solutions of the same concentration. It suggests that this difference is related to some characteristic of colloidal particles.

Colligative Properties and Particle Number

Colligative properties are directly proportional to the number of dissolved particles. Therefore, the smaller observed effect in colloidal solutions suggests a smaller effective number of particles when compared to true solutions.

Analyzing the Options

Consider each option: (a) Suspended in the medium affects dispersion, not colligative properties. (b) Lyophilic nature refers to affinity or interaction with the solvent, affecting stability, not colligative properties. (c) Fewer particles available for solute action due to aggregation or large surface area reduces colligative effect. (d) Surface area relates to adsorption and activities, not colligative properties directly.

Identifying the Correct Answer

The key factor affecting the difference in colligative properties is the number of solute particles. Large colloidal particles lead to fewer effective solute particles in the solution, affecting colligative properties.

Key concepts

Colloidal Solutions

Colloidal solutions, also known as colloids, are mixtures where one substance is dispersed evenly throughout another. This happens at a microscopic level. The dispersed particles in a colloid are larger than in a true solution, yet not large enough to settle out or to be seen with the naked eye. Colloids have unique properties due to their particle size. They exhibit the Tyndall effect, where light is scattered by the colloidal particles making the beam visible, similar to sunlight through mist.

Common examples of colloids include milk, fog, and gels. In chemistry, colloidal solutions are important because they display properties different from true solutions. Importantly, in a colloidal solution, the particles remain suspended and are fewer in number compared to true solutions. This affects colligative properties, emphasizing how colloids influence the concentration of particles in a medium.

Boiling Point Elevation

Boiling point elevation is a type of colligative property where the addition of a solute to a solvent increases the boiling point of the resulting solution. When a non-volatile solute is added, the vapor pressure of the solution decreases. This requires a higher temperature to reach the vapor pressure necessary for boiling, thus raising the boiling point.

The formula for boiling point elevation is given by \[ \Delta T_b = i \cdot K_b \cdot m \]where \( \Delta T_b \) is the boiling point elevation, \( K_b \) is the ebullioscopic constant, \( m \) is the molal concentration of the solution, and \( i \) is the van't Hoff factor, which denotes the number of particles the solute splits into when dissolved.

In colloidal solutions, the elevation of boiling point may be less markedly observed due to the relatively small number of discrete particles compared to true solutions.

Freezing Point Depression

Freezing point depression is another colligative property that occurs when the freezing point of a solvent decreases by adding a solute. Similar to boiling point elevation, this phenomenon happens because the solute particles interfere with the formation of the crystalline structure of the solvent, requiring a lower temperature to solidify.

The formula for calculating freezing point depression is:\[ \Delta T_f = i \cdot K_f \cdot m \]where \( \Delta T_f \) is the freezing point depression, \( K_f \) is the cryoscopic constant, \( m \) is the molal concentration, and \( i \) is the van't Hoff factor.

In colloidal solutions, the effect of freezing point depression is also minimized as the number of dispersed molecules available to disrupt the solvent's structure is smaller than in true solutions.

Vapor Pressure Lowering

Vapor pressure lowering occurs when a solute is dissolved in a solvent, causing the vapor pressure of the solution to decrease compared to the pure solvent. This is because the presence of solute particles at the surface reduces the number of solvent molecules that can escape into the vapor phase.

Raoult's law describes vapor pressure lowering quantitatively. According to Raoult's law: \[ P = X_1 \cdot P^{\circ}_1 \]where \( P \) is the vapor pressure of the solution, \( X_1 \) is the mole fraction of the solvent, and \( P^{\circ}_1 \) is the vapor pressure of the pure solvent.

In colloidal solutions, this effect is less pronounced than in true solutions because there are fewer solute particles affecting the solvent. The larger size of colloidal particles and their lower concentration means they exert less influence on the vapor pressure.