Problem 44 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is not related to colloids? (a) ultrafiltration (b) dialysis (c) Brownian movement (d) wavelength

Step-by-Step Solution

Answer

Option (d) wavelength is not related to colloids.

Step 1: Define Colloids

Colloids are mixtures where one substance of microscopically dispersed insoluble particles is suspended throughout another substance. These particles are small enough to remain suspended and do not settle out.

Step 2: Analyze ultrafiltration

Ultrafiltration is a process that uses a fine membrane to separate particles based on size. It is often used to purify colloids by removing solvated molecules like ions, while retaining larger colloidal particles.

Step 3: Evaluate dialysis as related to colloids

Dialysis is a process for separating molecules in solution by the difference in their rates of diffusion through a semipermeable membrane. It is commonly used to remove small ions from colloids while leaving the larger colloidal particles behind.

Step 4: Examine Brownian movement

Brownian movement refers to the random movement of particles suspended in a fluid. This is a characteristic behavior of colloids due to the collision of colloidal particles with the fast-moving molecules of the dispersion medium.

Step 5: Consider wavelength

Wavelength refers to the distance between successive crests of a wave, especially in sound or electromagnetic waves. It is generally not directly related to colloids but may affect phenomena like scattering which is due to particle interaction with light.

Step 6: Identify the unrelated option

Analyze each option to determine which is not a process or characteristic specifically related to colloids. While ultrafiltration, dialysis, and Brownian movement are directly related to colloid properties or processes, wavelength is not directly related to colloids themselves.

Key Concepts

Ultrafiltration

Ultrafiltration is a technique used to separate substances based on their particle size using a semi-permeable membrane. This process is crucial in the purification and concentration of colloidal dispersions. The membrane allows smaller molecules, like ions and solvents, to pass through while retaining larger colloidal particles.
Ultrafiltration offers several advantages for colloid purification:

• Efficient separation of large colloidal particles from the smaller impurities.
• Ability to purify substances without altering their chemical properties.
• Low energy consumption compared to other separation methods.

This technique is extensively used in industries, including pharmaceuticals and food processing, to ensure products meet purity standards. It’s also a pivotal process in water treatment systems where impurities need to be removed efficiently from water.

Dialysis in Chemistry

Dialysis is an essential process in chemistry used to separate molecules based on their diffusion rates through a semi-permeable membrane. This method is particularly useful in the purification of colloids.

How Dialysis Works

In dialysis, a mixture is placed in a compartment with a semi-permeable barrier. Smaller molecules move through the membrane into the outer dialysate solution based on concentration gradients, leaving behind large colloidal particles that cannot cross the barrier.
Key benefits of dialysis include:

• Precise separation of ions and small molecules from colloidal particles.
• Low risk of unintentional modification to the substances being separated.
• Wide application in biochemical research and industrial processes.

This technique is analogous to biological systems, similar to how kidneys function to purify blood by filtering waste products through natural membranes.

Brownian Movement

Brownian movement is the random motion of particles suspended in a fluid, emerging as a result of collisions with the fast-moving molecules of the dispersion medium. This erratic motion is a defining feature of colloids.

Origin and Significance

This phenomenon was first observed by botanist Robert Brown in 1827, detecting the independent motion of pollen grains in water. The constant and random movement helps prevent colloidal particles from settling out of the suspension, maintaining a uniform distribution.
Brownian movement is essential for:

• Understanding the stability of colloidal solutions.
• Providing insight into kinetic theories of molecules.
• Demonstrating the perpetual activity within fluid systems.

This random movement also conveys information about temperature, where higher temperatures lead to more intense Brownian motion due to increased kinetic energy of the particles.