Problem 161 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following colloids cannot be coagulaten easily? (a) Reversible colloids (b) Lyophillic colloids (c) Irreversible colloids (d) Lyophobic colloids

Step-by-Step Solution

Answer

Lyophilic colloids (b) cannot be coagulated easily due to their strong interactions with the solvent.

Step 1: Understanding Coagulation

Coagulation refers to the process where colloidal particles come together to form a larger aggregate, leading to sedimentation. Substances that can easily attract each other undergo coagulation more easily.

Step 2: Types of Colloids

There are two main types of colloids: lyophilic and lyophobic. Lyophilic (solvent-loving) colloids are stable in dispersion, while lyophobic (solvent-hating) colloids are less stable and more prone to coagulation.

Step 3: Reversible and Irreversible Colloids

Reversible colloids can return to their original state after coagulation if added to more solvent, typically associated with lyophilic colloids. Irreversible colloids, mainly lyophobic, cannot return to their original state after coagulation.

Step 4: Assessing Coagulation Ease

Lyophilic colloids form stronger interactions with the solvent, making them more stable and less prone to coagulation compared to lyophobic colloids. Therefore, they cannot be coagulated easily.

Key Concepts

Coagulation

Coagulation in the context of chemistry involves the process where colloidal particles,

• Which are very tiny particles dispersed in another medium,
• Combine to form clusters or aggregates.

This results in the particles settling out of the dispersion, forming a sediment.

Think of it as tiny particles gathering together to form a bigger clump. This occurs when forces attract these particles closer to one another, eventually leading to the precipitation of these aggregates.

The coagulation process is significant in various areas such as water purification, food science, and even in medical treatments. By inducing or controlling coagulation, we can separate components or purify substances effectively.

Lyophilic colloids

Lyophilic colloids, often called "solvent-loving" colloids, exhibit a high affinity for their solvent.

Characteristics:

• They form strong bonds with the solvent, making them very stable.
• Examples include gelatin, rubber, and starch which swell and disperse when mixed with water.
• These colloids can redistribute themselves easily in the solvent.

Lyophilic colloids are considered reversible because even if they coagulate, they can be returned to their original dispersed state by adding more solvent. They resist coagulation due to their strong interaction with the solvent molecules, which maintains their dispersed state.

Lyophobic colloids

Lyophobic colloids, in contrast to their lyophilic counterparts, do not interact well with the solvent. The term "lyophobic" essentially translates to "solvent-hating."

Key Points:

• They are unstable colloids and do not naturally form bonds with the solvent.
• Common examples include metals like gold and silver when dispersed in water.
• They tend to coagulate more easily because they lack the affinity that lyophilic colloids have with the solvent.

These colloids are typically formed using mechanical or chemical methods and are considered irreversible; once coagulated, they do not easily revert to their original state. Coagulating lyophobic colloids usually requires stabilizing agents or protective colloids to prevent them from collapsing.