Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

The movement of colloidal particles towards the oppositely charged electrodes on passing electric current is known as (a) Tyndall effect (b) cataphoresis (c) Brownian movement (d) none of these

Step-by-Step Solution

Answer

The movement described is known as cataphoresis (b).

Step 1: Understand the terms

Before choosing the correct answer, let's understand what each option means: - Tyndall Effect (Option a): This is the scattering of light by particles in a colloid or in a very fine suspension. - Cataphoresis (Option b): This is another term for electrophoresis, the movement of charged particles in a fluid under the influence of an electric field. - Brownian Movement (Option c): This is the random motion of particles suspended in a fluid, resulting from their collision with fast-moving molecules in the fluid.

Step 2: Relate the definition to the effect

The question describes the movement of colloidal particles towards oppositely charged electrodes when an electric current is applied. This specific movement of charged particles under an electric field is a characteristic of cataphoresis (or electrophoresis).

Step 3: Eliminate incorrect options

Given the descriptions: - The Tyndall effect does not describe any movement but rather the scattering of light. - Brownian movement describes random motion, not directed movement towards electrodes. - Therefore, these two cannot be the answer.

Step 4: Verify the correct option

The definition given in the question aligns perfectly with the concept of cataphoresis, where colloidal particles move under the influence of an electric field towards oppositely charged electrodes. Hence, the correct answer is Option b.

Key Concepts

Colloidal particles

Colloidal particles are tiny particles that are dispersed throughout another substance, forming what is known as a colloid. These particles are larger than molecules, but small enough to be suspended within a medium without settling at the bottom. Colloids are found in many forms in everyday life, such as in milk, fog, and whipped cream. These particles are typically in the range of 1 to 1000 nanometers in size.
Within a colloid, particles do not settle due to gravity because they are subject to forces like Brownian motion, which is the erratic movement resulting from collisions with molecules of the surrounding medium. In addition to this, colloidal particles can carry electric charges that result in forces of repulsion or attraction between them.
Colloids can exhibit unique behaviors under different conditions, such as scattering light in the Tyndall effect or moving in response to electric fields, known as electrophoresis. This movement is particularly significant when studying the effects of electric current on colloidal particles.

Electric current effects

When an electric current is applied to a colloid, it can have significant effects on the particles within the colloid.

• One notable effect is electrophoresis, which describes the movement of charged particles under the influence of an electric field.
• This process occurs as charged particles are attracted towards an electrode of the opposite charge. For instance, positively charged particles will move towards the negative electrode and vice versa.

Electric currents can alter the stability of colloidal suspensions. This change occurs because the application of the current can decrease the repulsive forces between like-charged particles, consequently promoting aggregation. The utility of this phenomenon is remarkable in many fields, such as biochemistry and materials science, where electrophoresis is often used to separate different particles based on their charge and size.
Understanding these effects is crucial for manipulating and controlling the behavior of colloidal suspensions in practical applications.

Movement in electric fields

The movement of colloidal particles in electric fields is defined by a process known as electrophoresis. This term also refers specifically to the diaspora of particles in a fluid or gel as they are subjected to an electric field. Electrophoresis has practical applications in laboratory and industrial settings. Upon applying an electric field, colloidal particles, due to their charge, accelerate towards the electrode with the opposite charge. The rate at which they move depends on several factors:

• The magnitude of the charge on the particles.
• The viscosity of the medium through which they are moving.
• The strength of the electric field applied.

This movement allows for the separation and analysis of particles, such as in DNA separation during gel electrophoresis.
Navigating this process accurately is vital for applications where precise separation and analysis of particle size and charge distributions are required. The capability to direct such particle movements is not only critical in scientific research but also in various industrial processes where colloidal dispersions are utilized.