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

The solvent hating colloids are lyophobic.

Step 1: Understand the Terms

First, it's important to understand what each of these terms means. 'Lyophilic' colloids are those that have an affinity for the solvent, meaning they are solvent loving. On the other hand, 'lyophobic' colloids have a repulsion for the solvent, meaning they are solvent hating. 'Hydrophilic' refers to colloids that have an affinity for water (the solvent, if it is water).

Step 2: Identify the Solvent Hating Option

Now that we've established the definitions, we can identify that 'lyophobic' is the one that refers to solvent hating colloids. This means lyophobic colloids do not have an affinity for the solvent.

Step 3: Verify by Elimination

Eliminating the options, 'lyophilic' cannot be the answer because it is solvent loving. Similarly, 'hydrophilic' cannot be the answer in this context because it refers to water-loving, which is a type of solvent affinity. 'None of these' is also incorrect because a correct option exists (lyophobic).

Key Concepts

Lyophilic Colloids

Lyophilic colloids are fascinating in the way they naturally interact with solvents. The term "lyophilic" comes from the Greek words "lyo" (meaning dissolve) and "philic" (meaning loving). Therefore, lyophilic colloids are known as solvent-loving colloids. This strong attraction to the solvent means that when mixed, the particles readily disperse and form stable, homogeneous mixtures.

One notable property of lyophilic colloids is their ability to absorb large amounts of water without breaking apart. This quality leads to a very stable colloidal solution, often requiring substantial energy or effort to separate. Gelatin and starch, when mixed with water, serve as classic examples of lyophilic colloids. They can create gels or solutions where the particles are so well mixed that you can't see them with the naked eye.

Key Characteristics of Lyophilic Colloids:

• High stability in solution; they rarely precipitate out.
• Can form sols or gels depending on concentration.
• Easily reversed from gel to sol state with minor changes (temperature or solvent).

Understanding lyophilic colloids can give insights into how some everyday materials function, explaining why certain mixtures are naturally more stable than others.

Lyophobic Colloids

Lyophobic colloids present a challenging yet intriguing aspect of colloid chemistry, as these colloids naturally repel solvents. Derived from "lyo" (dissolve) and "phobic" (fearing), lyophobic colloids do not easily dissolve in the solvent. This means that they don't have a natural affinity toward the solvent, resulting in less stable solutions or dispersions.

Since lyophobic colloids do not interact favorably with their solvent, creating stable dispersions typically requires special treatment or additives, known as stabilizing agents, to prevent the particles from aggregating and settling out of the solution. For instance, metal sols or sulfur sols are examples of lyophobic colloids often requiring stabilizers to maintain their dispersion.

Key Characteristics of Lyophobic Colloids:

• Low stability; they tend to precipitate rapidly without stabilizers.
• Formed by mechanical methods or condensation techniques.
• More sensitive to electrolytes compared to lyophilic colloids.

The behavior of lyophobic colloids is critical in industrial applications such as paints and inks, where stability of the colloid is a crucial factor for product quality.

Hydrophilic Colloids

Hydrophilic colloids specifically describe colloidal particles with a strong affinity to water as the solvent. The word "hydrophilic" directly translates to "water-loving," indicating that these substances mix well with water. When introduced to water, hydrophilic colloids disperse easily, and the resulting colloidal dispersion is typically homogeneous and stable.

The water affinity in hydrophilic colloids is due to the hydrogen bonding with water molecules. Common substances that form hydrophilic colloids include proteins, gums, and algae extracts. For instance, certain types of proteins and plant polysaccharides can create stable colloid systems that are utilized in food technology and pharmaceuticals to modify textures or stabilize emulsions.

Key Characteristics of Hydrophilic Colloids:

• High water affinity due to hydrogen bonding.
• Capable of reversible gel-sol transitions with changes in temperature or pH.
• Used prominently in food, cosmetics, and drug formulations for their stabilizing abilities.

Understanding hydrophilic colloids is essential for applications that require the maintenance of texture and consistency, which are pivotal in many food products and pharmaceutical formulations.