Problem 60 - A Complete Resource Book in Chemistry for JEE Main

Question

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

Step-by-Step Solution

Answer

(b) adding electrolyte

Step 1: Understanding Colloid Destruction

Colloids are mixtures where the particle size is intermediate between true solutions and suspensions. Destroying colloids generally involves methods to alter their stability, such as adding substances to change the interaction between particles.

Step 2: Option Analysis: Ultrafiltration

Ultrafiltration is a method to separate particles based on size. It involves forcing the colloid through a membrane that retains larger particles while letting smaller ones pass, but it does not chemically alter the colloid.

Step 3: Option Analysis: Adding Electrolyte

Adding an electrolyte to a colloid can neutralize the charge on the colloidal particles. This neutralization decreases the repulsion between particles, allowing them to coalesce and precipitate, which effectively destroys the colloid.

Step 4: Option Analysis: Using Both Methods

Using both ultrafiltration and adding an electrolyte could together help in the destruction of colloids, though ultrafiltration alone is not sufficient for actual destruction.

Step 5: Option Analysis: Dialysis

Dialysis is a separation process that involves diffusion through a semipermeable membrane, mainly used to remove small ions or molecules from large colloidal particles. It does not destroy colloids but separates components.

Step 6: Identifying the Correct Answer

Among the options, adding electrolytes directly leads to the destruction of colloids by precipitating them out of the dispersion medium. Thus, the correct choice is adding electrolyte.

Key Concepts

Ultrafiltration in Colloidal Mixtures

Ultrafiltration is a powerful technique for separating particles from a colloidal mixture based on their size. This method utilizes a semipermeable membrane that allows smaller particles or molecules to pass through, while larger ones are retained. Unlike true destruction, ultrafiltration does not chemically alter or decompose the colloid.

Here are some key points about ultrafiltration:

• It involves a physical barrier like a membrane filter.
• Separation is based solely on particle size.
• Large particles or impurities are retained by the membrane.
• It is effective for concentrating or removing specific sizes of particles without altering their chemical structure.

Ultrafiltration is commonly used to purify or concentrate colloids, rather than destroy them. Its primary role is to separate components, making it an essential tool in various industries and laboratories. While an important technique, it cannot, on its own, lead to the destruction of a colloid.

Role of Adding Electrolytes in Colloidal Systems

Adding electrolytes to a colloidal system plays a crucial role in the destabilization and "destruction" of colloids. Electrolytes are substances that release ions when dissolved in water, and these ions can significantly alter the properties of colloidal particles.

Key effects of adding electrolytes include:

• Neutralization of Electrical Charges: Electrolyte ions can neutralize the surface charges on colloidal particles, reducing repulsion.
• Enhanced Coagulation: Neutralized charges allow particles to come closer, sticking together and eventually precipitating out.
• Effect on Stability: High concentrations of electrolytes can lead to rapid coagulation, effectively destabilizing the colloidal system.

In essence, the addition of an electrolyte facilitates the aggregation of colloidal particles, leading them to settle out of the solution. This process is utilized in water treatment and other applications where the removal of colloidal impurities is required. Thus, it is a direct method for colloid destruction.

Understanding Dialysis in Colloids

Dialysis is a separation technique that uses a semipermeable membrane to separate smaller molecules or ions from larger colloidal particles. Although dialysis does not destroy colloids, it serves an important function in purifying them by removing unwanted small particles.

Some important points about dialysis include:

• Separation Process: The semipermeable membrane allows only small ions or molecules to pass through, retaining larger colloidal particles inside.
• Purification Function: Dialysis helps in cleaning the colloid by removing impurities like small ions.
• Clear Solution: After dialysis, the colloid remains intact while the solution becomes clearer and purer.

This process is particularly useful in biochemistry and medical applications, such as purifying proteins or removing waste products from blood in kidney treatments. Unlike adding electrolytes, dialysis is about separation and purification, not the destruction of the colloid itself.