Problem 117 - A Complete Resource Book in Chemistry for JEE Main

Question

Lyophilic sols are more stable than lyophobic sols because the particles (1) are positively charged (2) are negatively charged (3) are solvated (4) repel each other (5) are heavy (a) 2,3 and 4 (b) 2 and 3 (c) 1,2 and 5 (d) 3 only

Step-by-Step Solution

Answer

Option (d) 3 only is correct because lyophilic sols are stabilized by solvation.

Step 1: Identify Sol Types

Understand that lyophilic sols are colloids with dispersed phase particles that have an affinity for the solvent, whereas lyophobic sols do not have this affinity for the solvent.

Step 2: Recognize Stability Factors

Recall that lyophilic sols are more stable than lyophobic sols because their particles are solvated, meaning they are surrounded and stabilized by a layer of solvent molecules.

Step 3: Analyze Options Given

Evaluate the options provided: (1) and (2) concern charges, (3) refers to solvation, (4) mentions repulsion, and (5) concerns the weight of particles. In contrast, the stability of lyophilic sols mainly depends on solvation.

Step 4: Match Factors with Options

Find that the solvation of particles (option 3) is essential for the stability of lyophilic sols. Other factors like charge or weight are not primarily relevant to this characteristic stability.

Step 5: Select the Correct Answer

Conclude that the correct choice for why lyophilic sols are more stable than lyophobic sols is "3 only," which corresponds to solvation.

Key Concepts

Lyophilic Sols

Lyophilic sols, also known as "solvent-loving" sols, consist of colloidal particles with a strong affinity for the solvent they're in. This affinity results in a significant interaction between the dispersed phase and the solvent. Because of this inherent attraction, lyophilic sols are highly stable. When the particles are introduced into a solvent, they become substantially solvated, which means they are surrounded by solvent molecules.

Here's why that matters:

• Solvation creates a protective layer around each particle. This layer prevents the particles from coming too close and aggregating, which means they remain stable and dispersed over time.
• Lyophilic sols do not require additional stabilizers or surfactants to maintain this stability because the solvent interaction is inherently strong.

In practical applications, lyophilic sols are utilized in areas where stability and consistency of the sol are crucial, like in certain food products and pharmaceuticals. Their stability is primarily attributed to solvation, highlighting the influence of particle-solvent interaction on colloidal stability.

Lyophobic Sols

Lyophobic sols, or "solvent-hating" sols, involve particles that lack attraction to the solvent. This absence of affinity makes them inherently less stable than lyophilic sols. In lyophobic sols, the stability is often reliant on external factors such as electrical charges or the use of surfactants to prevent the particles from aggregating.

Key attributes include:

• Lyophobic sols depend heavily on the repulsion between charged particles for stabilization. Without it, particles tend to clump together easily.
• The process of making lyophobic sols stable requires more external intervention, like adding electrolytes or physical agitation.

Due to their lack of inherent stability, lyophobic sols are more challenging to work with in both industrial and laboratory settings. This requirement for additional stabilization methods makes them less favorable when consistent and long-term stability is required.

Solvation

Solvation is a critical concept when we talk about the stability of colloidal systems, especially in the context of lyophilic sols. Solvation occurs when solvent molecules closely associate with solute particles, effectively surrounding them. This process is fundamental for maintaining the structure and stability of the sol.

Why it's important:

• In lyophilic sols, solvation results in a stable colloid because the solvent molecules create a barrier around each particle, preventing aggregation.
• This shielding effect significantly reduces the chance of particles clustering together, which results in a uniform and stable mixture.

The process of solvation is dictated by the chemical properties of both the solute and the solvent, including polarity and potential hydrogen bonding capability. In colloid chemistry, understanding and manipulating solvation are essential for designing stable colloidal systems.

Stability Factors in Colloids

Stability in colloids is determined by several interdependent factors. These factors decide whether the colloid remains evenly mixed or if the dispersed particles will congregate over time, resulting in an unstable system.

Main factors include:

• Solvation: The previously discussed solvation layer provides significant stability, especially in lyophilic sols, by inhibiting particle aggregation.
• Charge: Electrostatic charges on particles can create repulsive forces that help to maintain distance between them, leading to increased stability in lyophobic systems.
• Particle Size: Smaller particles generally lead to more stable colloids as gravity exerts less influence over them, reducing the likelihood of sedimentation.

Each colloid type may rely more heavily on certain stability factors over others. While lyophilic sols lean significantly on solvation, lyophobic sols often require an engineered balance of charge and size to achieve and maintain stability. Understanding these factors is crucial in fields like material science and pharmaceuticals, where stable colloids are essential.