Question

Which of the following is used for the destruction of colloids? (a) ultrafiltration (b) adding electrolyte (c) both (a) and (b) (d) dialysis

Short answer

Adding electrolytes (option b) is used for the destruction of colloids.

Step-by-step solution

Understanding the Problem

There are different methods to destroy colloids, and the task is to identify which of the given options are used for this purpose. The options include ultrafiltration, adding an electrolyte, both ultrafiltration and adding an electrolyte, and dialysis.

Evaluating Option (a): Ultrafiltration

Ultrafiltration is a pressure-driven separation process that removes particles from a solution, including colloids. However, it removes rather than destroys colloidal particles. It is more of a purification method rather than a destruction method.

Evaluating Option (b): Adding Electrolyte

Adding electrolytes to a colloidal solution can cause coagulation or precipitation of the colloids, leading to their destruction. This occurs due to the neutralization of charges on the colloid particles, which allows them to clump together and settle out of the solution.

Evaluating Option (c): Both (a) and (b)

For option (c) to be correct, both ultrafiltration and adding an electrolyte must destruct colloids. However, ultrafiltration mainly separates rather than destroys colloids. Therefore, option (c) is incorrect because ultrafiltration is not a destruction method.

Evaluating Option (d): Dialysis

Dialysis allows for the separation of smaller molecules and ions from colloids but does not destroy colloids. It primarily purifies the solution by removing small solutes, leaving the colloidal particles intact. Therefore, it is not a destruction method.

Selecting the Correct Answer

The correct method for the destruction of colloids is adding an electrolyte, as it causes coagulation and destruction by neutralizing colloid charge, whereas ultrafiltration and dialysis serve different purposes.

Key concepts

Ultrafiltration

Ultrafiltration is a method that uses pressure to push a liquid through a semi-permeable membrane, thereby removing suspended particles, such as colloids. This process is frequently used in water purification and in various industries to remove impurities from solutions. Ultrafiltration primarily acts as a physical separation technique.

Rather than destroying colloidal particles, this technique merely separates them from the rest of the solution. The semi-permeable membrane traps the larger particles due to their size, while allowing smaller ions and molecules to pass through.

This results in a purified fluid, free of colloidal size particles, but the colloidal particles themselves are not chemically altered or "destroyed" in the process. As such, while ultrafiltration is an effective purification process, it is not categorized as a destruction method.

Electrolyte Coagulation

Adding electrolytes to a colloidal solution is an effective method for the destruction of colloids through a process known as coagulation. When electrolytes are added to the solution, they impact the electric charges on the surface of the colloid particles. This process causes several reactions in the solution:

• Neutralization of charged particles: The charges on the colloidal particles are neutralized by the ions from the electrolytes.
• Reduction in electrostatic repulsion: With reduced repulsive forces, colloid particles can move closer to each other.
• Coagulation: The particles clump together and form larger aggregates (flocs), which precipitate from the solution.

This process effectively destructs the colloidal system, as the suspended particles lose their stability and are removed from the solution as a sediment. It’s widely used in water treatment plants and several industrial applications to clear colloidal suspensions from liquids.

Dialysis

Dialysis is a separation process used mainly to remove small molecules and ions from colloidal solutions. It involves the use of a semi-permeable membrane, similar to ultrafiltration, to differentiate between colloidal particles and smaller solute molecules.

However, the key difference is its function in purifying the mixture. While smaller solute particles and ions diffuse through the membrane into the surrounding solution, the larger colloidal particles cannot pass through and remain in the solution.

This makes dialysis effective for separating different components in a solution but not for destroying colloids. The colloids remain largely unchanged and are not aggregated or precipitated in the procedure. Thus, dialysis is not a method used for the destruction of colloids, but rather for their purification by removing unwanted smaller solutes.