Problem 163 - A Complete Resource Book in Chemistry for JEE Main

Question

Which phenomenon occurs when electric field is applied to a colloid solution and electrophoresis is prevented. (a) Electroosmosis takes place (b) Reverse osmosis takes place (c) Dispersion medium becomes stationary (d) Dispersion medium begins to move

Step-by-Step Solution

Answer

(a) Electroosmosis takes place.

Step 1: Understanding the Problem

We need to determine the phenomenon that occurs when an electric field is applied to a colloid solution, and electrophoresis is not allowed to happen. This involves examining the behavior of the dispersion medium and the colloidal particles under these conditions.

Step 2: Recap of Key Concepts

In a colloidal system, electrophoresis refers to the movement of dispersed particles through a stationary medium under the influence of an electric field. If electrophoresis is prevented, another phenomena could involve the movement of the fluid itself.

Step 3: Identifying Electroosmosis

When electrophoresis is prevented but an electric field is applied, electroosmosis may occur. In electroosmosis, the dispersion medium (usually the liquid) moves relative to the stationary colloidal particles under the influence of the electric field.

Step 4: Matching with Options

Given the options: (a) Electroosmosis takes place, (b) Reverse osmosis takes place, (c) Dispersion medium becomes stationary, and (d) Dispersion medium begins to move, the most accurate description for the movement of the dispersion medium under the electric field influence, when electrophoresis is prevented, is option (a) Electroosmosis takes place.

Key Concepts

Colloid Solution

A colloid solution is a type of homogeneous mixture where one substance is dispersed evenly throughout another. The substances in a colloid are considered to be in different phases, such as solid, liquid, or gas. But the key feature of a colloid is that the particles do not settle out under normal conditions.
A colloidal system consists of the dispersed phase and the continuous phase, also known as the dispersion medium. The dispersed phase represents the individual droplets or particles distributed within the dispersion medium.
For example, milk is a colloid where fat droplets are spread in water. Another common example is fog, where tiny water droplets are dispersed in air. Colloids are important in everyday products and can be found in food, cosmetics, and industrial processes.

Electrophoresis

Electrophoresis is a process where charged particles are moved through a stationary fluid or gel under the influence of an electric field. The charge on the particles causes them to move toward the electrode with the opposite charge.
In the context of colloid solutions, electrophoresis typically involves the dispersed particles, which may carry an electrical charge. When exposed to an electric field,

• positively charged particles are attracted to the cathode (negative electrode), while
• negatively charged particles are attracted to the anode (positive electrode).

Electrophoresis is widely used in scientific applications, such as DNA analysis and protein separation. But in the exercise scenario, this movement is intentionally prevented to allow for the observation of other phenomena, like electroosmosis.

Dispersion Medium

The dispersion medium in a colloid solution is the phase in which the particles of the dispersed phase are distributed. It provides a continuous pathway that allows the dispersed particles to remain evenly distributed.
Depending on the type of colloid, the dispersion medium can either be a liquid, gas, or solid. In a colloidal system like jelly, water serves as the dispersion medium for the gelatin particles.
When an electric field is applied to a colloid and electrophoresis is blocked, the dispersion medium itself may start to move due to electroosmosis. This is distinct from electrophoresis, where it is the dispersed particles that move. Hence, identifying the behavior of the dispersion medium is crucial in understanding what occurs under such conditions.

Electric Field

An electric field is a force field surrounding electrically charged particles. It represents the effect that an electric charge has on other charges in the space around it.
When applied to a colloid solution, an electric field can exert forces on both the dispersed particles and the dispersion medium. This can induce motion by influencing the charged particles.

• If electrophoresis is allowed, it's the charged particles that move.
• If it's prevented, the electric field still acts on the dispersion medium, potentially causing it to move, as seen in electroosmosis.

The concept of electric fields is essential in many technological and scientific applications, highlighting how charged particles interact and move in various substances.