Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

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

Step-by-Step Solution

Answer

(a) lyophilic and (c) hydrophilic.

Step 1: Understand the Terms

To solve this exercise, we need to understand the terms used in the question: 'lyophilic' and 'lyophobic.' 'Lyophilic' colloids are solvent-loving, meaning they have an affinity for the solvent, while 'lyophobic' colloids do not like the solvent, meaning they have little to no attraction to it. 'Hydrophilic' is specifically a type of lyophilic colloid that is water-loving.

Step 2: Analyze the Options

Now, let's look at the options given: - (a) Lyophilic: These colloids have a strong attraction to the solvent and are therefore solvent-loving. - (b) Lyophobic: These colloids dislike the solvent and are not solvent-loving. - (c) Hydrophilic: These are a subtype of lyophilic colloids, specifically solvent-loving in water.

Step 3: Select the Correct Option

Considering the meanings described, the correct answer to which colloids are solvent loving is both option (a) lyophilic and option (c) hydrophilic, as hydrophilic refers specifically to water loving in the context of solvents.

Key Concepts

Lyophilic Colloids

Lyophilic colloids are known as solvent-loving colloids. The term 'lyophilic' comes from the Greek words 'lyo', meaning to dissolve, and 'philic', meaning having an affinity for. This makes lyophilic colloids unique because they have a natural attraction to the solvent in which they are dispersed.

These colloids readily dissolve in the solvent and form stable solutions. For example, when you add gelatin or starch to water, they easily mix and create a consistent colloidal dispersion.

• They have a high affinity for the solvent.
• The resulting colloidal solutions are often quite stable.
• The solutions have low surface tension, increasing their stability.

One major advantage of lyophilic colloids is that they are reversible. You can remove them from the solution and later combine them again without losing any of their original properties. This makes lyophilic colloids highly valuable across various industries, from food production to pharmaceuticals.

Lyophobic Colloids

Lyophobic colloids, in contrast to lyophilic colloids, are solvent-hating or solvent-avoiding colloids. The word 'lyophobic' is derived from 'lyo', meaning dissolve, and 'phobic', meaning a fear of. Lyophobic colloids do not mix easily with the solvent; hence, they only form a colloidal suspension with special techniques or treatments.

These might include significant mechanical energy input or the use of specific additives to help sustain the dispersion. Examples of lyophobic colloids are sols made of metals like silver or gold.

• Lack a natural affinity for the solvent.
• Often need stabilizers to prevent the particles from aggregating.
• Are generally less stable than lyophilic colloids.

Since they are thermodynamically unstable, their cohesive forces are greater than their adhesive forces with the solvent, making them susceptible to precipitation without external stabilization. Thus, industries must carefully control the environment in which lyophobic colloids are used.

Hydrophilic Colloids

Hydrophilic colloids form a subset of lyophilic colloids that specifically deal with water as the solvent. 'Hydrophilic' stems from 'hydro', meaning water, and 'philic', meaning loving. As you might guess, these colloids have a strong affinity for water, which means they dissolve easily in it to form stable colloidal dispersions.

They are important due to their ability to stabilize through hydrogen bonding with water molecules. Common examples of hydrophilic colloids include proteins, agar, and gelatin.

• Exhibit strong interactions with water.
• Form stable dispersions or gels in aqueous solutions.
• Often used in biological and food industries due to their compatibility with water.

The ability to disperse easily in water and form stable colloids makes hydrophilic colloids pivotal in many applications, especially in food processing where moisture retention and stabilization are essential.