Problem 59 - A Complete Resource Book in Chemistry for JEE Main

Question

The capacity of an ion to coagulate a colloidal solution depends upon (a) nature of charge (b) amount of charge (c) its shape (d) both (a) and (b)

Step-by-Step Solution

Answer

The capacity depends on both the nature of charge and amount of charge, so the answer is (d).

Step 1: Understand the Factors

Colloidal solutions are often stabilized by electric charges on particles. The capacity of an ion to destabilize or coagulate them depends on certain key factors.

Step 2: Consider the Nature of Charge

The nature of the charge carried by colloidal particles and ions is crucial. Ions carrying opposite charges to those on the colloidal particles will attract them, leading to coagulation.

Step 3: Evaluate the Amount of Charge

The higher the charge on the ion, the stronger its ability to neutralize the charge on colloidal particles, thus promoting coagulation.

Step 4: Analyze Shape Influence

While shape can influence interactions, it is not a primary factor for coagulation in comparison to charge properties.

Step 5: Combine Findings

Given that both (a) nature of charge and (b) amount of charge are critical for coagulation, both must be considered together.

Key Concepts

Nature of Charge in Colloids

Colloids are mixtures where tiny particles are dispersed within a continuous medium. These particles often carry an electric charge, either positive or negative. The charge on these colloidal particles plays a vital role in keeping them stable. For instance, if the colloidal particles are negatively charged, they repel each other, preventing them from clumping together. This repulsion is what keeps the colloidal solution stable and well-dispersed.

The coagulation, or clumping together, of colloidal particles often occurs when an ion with a charge opposite to that of the particles is introduced. For example, positively charged ions can attract and neutralize negatively charged colloidal particles, causing them to group together. This phenomenon explains why the nature of the charge on both the colloidal particles and the ions is crucial. Understanding this interaction helps us predict and control the stability of colloidal solutions.

Amount of Charge in Coagulation

While the nature of the charge is essential, the amount of charge carried by ions also significantly impacts the coagulation process. The greater the charge on an ion, the stronger its ability to attract and neutralize the opposite charge on colloidal particles.

For instance:

• Ions with a higher charge magnitude can more effectively drive the coagulation process than ions with a lesser charge.
• A single, highly charged ion can neutralize multiple colloidal particles effectively.

The coagulating power of such ions is explained by the Schulze-Hardy rule. According to this rule, multivalent ions play a more dominant role in precipitating colloids than monovalent ions. Simply put, when it comes to coagulation, **more charge means more impact**.

Colloidal Stability

The stability of colloidal solutions is maintained through several mechanisms, primarily through the charges on the colloidal particles. These charges create a force of repulsion between particles, preventing them from clumping together. However, stability is not solely reliant on charge.

Other factors include:

• The size and distribution of the particles: Uniformly sized particles tend to remain more stable.
• The medium in which colloidal particles are dispersed: A medium with properties conducive to stability, like an appropriate pH level, supports colloidal stability.

Keeping a colloid stable means ensuring that these factors work together to maintain dispersion. By managing these elements, we can control the stability of colloidal solutions, which is crucial in various applications across industries from food to medicine.