Problem 28 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following colloids are solvent hating? (a) lyophilic (b) lyophobic (c) hydrophilic (d) none of these

Step-by-Step Solution

Answer

Lyophobic colloids are solvent hating.

Step 1: Understanding the Terms

We begin by understanding the definition of **lyophilic** and **lyophobic** colloids. Lyophilic colloids are solvent-loving, which means they are attracted to the solvent and mix easily. Examples include gelatin and starch. On the other hand, lyophobic colloids are solvent-hating. They have little attraction to the solvent, and tend not to mix easily without added stabilizers.

Step 2: Analyzing the Options

Now, let's examine the options: (a) Lyophilic colloids - These are **solvent-loving**, not solvent-hating. (b) Lyophobic colloids - These are **solvent-hating** by definition. (c) Hydrophilic – This term means water-loving, which suggests compatibility with water. (d) None of these - This option would be correct if no other options were suitable.

Step 3: Identifying the Correct Answer

Given these definitions and analysis, the colloid that is explicitly solvent-hating is **lyophobic**. Therefore, option (b) is the correct answer.

Key Concepts

Lyophobic Colloids

Lyophobic colloids can be understood as the type of colloids that are known to resist mixing with the solvent. They derive their name from the Greek words 'lyo' meaning to loosen or dissolve, and 'phobic' meaning fearing. Thus, they are often referred to as solvent-hating. This characteristic is because these colloids have little to no affinity for the solvent.
They require the presence of stabilizers to maintain their dispersion in the solvent. Without these stabilizers, they are prone to aggregation or settling out of the mixture. Some common examples of lyophobic colloids include metal sols such as gold or silver sol in water.

• They do not form spontaneously. Energy input is needed to initiate dispersion.
• They often require external agents for stabilization.
• The stability of these colloids heavily depends on the charge on the particles and the presence of adsorbed layers.

Overall, understanding the nature and behavior of lyophobic colloids is crucial for their applications, especially in fields like materials science and industrial chemistry.

Lyophilic Colloids

In stark contrast to lyophobic colloids, lyophilic colloids are often termed solvent-loving. They have a strong affinity towards the solvent, which allows them to mix and disperse readily in a solvent without the need for additional stabilizers. The term 'lyophilic' comes from the Greek words 'lyo' meaning to dissolve, and 'philic' meaning loving, highlighting their compatibility with solvents.
These colloids are characterized by the ease with which they form stable colloidal dispersions. They naturally form when certain substances interact with specific solvents. Gelatin, gum arabic, starch, and proteins in water are classic examples.

• Spontaneously form colloidal dispersions by dissolving in the solvent.
• High stability due to strong intermolecular interactions between the colloid particles and the solvent.
• They can often be easily reconstituted if dried and redispersed in the solvent.

Their ability to easily form stable dispersions makes them immensely useful in biological and industrial applications, such as in food products, pharmaceuticals, and cosmetics.

Solvent Interaction in Colloids

The interactions between colloids and solvents define much of their behavior and properties. Solvent interaction in colloids can be thought of as the degree to which colloidal particles are either attracted to or repelled by the solvent.
The interaction between colloids and solvents is not purely physical but involves several factors:

• Chemical nature: Compatibility of the chemical nature of the colloid and solvent influences stability and formation.
• Electrostatic forces: Charges present on colloidal particles and in the solvent can create repulsion or attraction that stabilize or destabilize the colloid.
• Solvent polarity: The polarity of the solvent can significantly affect how colloids interact with it; polar solvents interact more strongly with polar colloids.

An understanding of solvent interaction in colloids is vital not only for predicting the behavior of colloids in different environments but also for modifying them for specific applications. This knowledge is essential in areas such as drug delivery, paints, and coatings, where controlled stability and interaction of colloids play a critical role.