Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a lyophillic colloidal solution? (a) aqueous starch solution (b) aqueous protein solution (c) gold sol (d) polymer solutions in some organic solvents

Step-by-Step Solution

Answer

Aqueous protein solution.

Step 1: Understanding Lyophilic Colloids

Lyophilic colloids are colloidal systems in which the dispersed phase has a strong affinity for the dispersion medium, resulting in the formation of a stable colloid. These types of colloids are also known as 'solvent-loving' colloids.

Step 2: Examine Each Option

- (a) Aqueous starch solution: Starch can absorb water and swell, forming a lyophilic colloid. - (b) Aqueous protein solution: Proteins dissolve in water and interact well with it, forming a lyophilic colloid. - (c) Gold sol: This is a lyophobic colloid because gold particles do not have a strong affinity for the medium. - (d) Polymer solutions in some organic solvents: Depending on the polymer and solvent, these can be lyophilic if the polymer has a strong affinity for the solvent.

Step 3: Compare and Identify the Strongest Lyophilic Colloid

Both starch and proteins are known for forming lyophilic colloids. However, proteins generally have a stronger affinity and broader solubility in water due to their complex structure and variety of intermolecular forces.

Key Concepts

Colloidal Solutions

Colloidal solutions are unique mixtures where one substance (called the dispersed phase) is distributed evenly within another substance, often referred to as the dispersion medium. Unlike true solutions, colloidal solutions do not dissolve at the molecular level; instead, the particles are suspended throughout the medium, usually measuring between 1 to 1000 nanometers. This creates a system where the particles remain as tiny as microscopic specks, yet large enough to scatter light, which is why colloids often appear cloudy.

• Dispersed Phase: The substance that is dispersed in the colloidal solution.
• Dispersion Medium: The substance in which the dispersed phase is distributed.

Usually, colloidal solutions occur naturally but can also be engineered for various industrial and scientific purposes. Depending on the nature of the dispersed phase and the dispersion medium, colloidal solutions can exhibit fascinating properties such as stability, the ability to be easily reconstituted or transformed, and reactivity to external conditions such as temperature and pH.

Dispersed Phase

The dispersed phase in a colloidal solution comprises the particles that are distributed throughout the dispersion medium. Think of it as the 'floating' component in the mixture, somewhat like the sugar particles in a cup of tea, except they do not dissolve entirely. Instead, they maintain their individuality and contribute to the unique properties of colloidal solutions.
A distinctive feature of the dispersed phase is its size, typically ranging from 1 to 1000 nanometers. This tiny size is crucial because it determines how the colloidal solution will behave and interact with light, like causing the Tyndall effect, which is the scattering of light by the particles within the colloid.
The chemical nature of the dispersed phase also plays a crucial role in defining the stability and reactivity of the colloidal solution, often interacting with the dispersion medium through various forces such as van der Waals forces or electrostatic forces. These interactions are essential for determining whether the colloid will be lyophilic or lyophobic.

Affinity for Dispersion Medium

Affinity for the dispersion medium is a critical concept for understanding colloidal solutions, as it defines whether a colloid is classified as lyophilic or lyophobic. Affinity refers to how well the dispersed phase interacts with the medium.
In lyophilic colloids:

• The dispersed particles have a strong affinity for the dispersion medium.
• The formation of the colloid is spontaneous and easy because of the attractive interactions.

Lyophilic means 'solvent-loving', so these colloids are generally stable and can often be reconstituted by simply adding the dispersion medium, making them useful in applications such as food, cosmetics, and pharmaceuticals.
On the other hand, lyophobic colloids have little to no attraction to the medium. This means they often require additional agents or specific conditions to stabilize the colloid, which makes them less naturally stable compared to their lyophilic counterparts. Understanding a colloid's affinity for its medium is essential for applications where stability and ease of formation are critical.