Problem 192 - A Complete Resource Book in Chemistry for JEE Main

Question

Gold numbers of protective colloids \(\mathrm{A}, \mathrm{B}, \mathrm{C}\) and \(\mathrm{D}\) are \(0.50,0.01,0.10\) and \(0.005\), respectively. The correct order of their protective powers is [2008] (a) \(\mathrm{D}<\mathrm{A}<\mathrm{C}<\mathrm{B}\) (b) \(C

Step-by-Step Solution

Answer

The correct order is (c) A < C < B < D.

Step 1: Understanding Gold Numbers

The gold number is a measure of the protective power of a colloid. A lower gold number means that less colloid is needed to stabilize a gold sol, indicating a higher protective power.

Step 2: Listing Given Gold Numbers

The gold numbers for the colloids are given as follows: - Colloid A: 0.50 - Colloid B: 0.01 - Colloid C: 0.10 - Colloid D: 0.005

Step 3: Determining Protective Power Order

To determine the protective power, list the colloids in order of increasing gold numbers, because a lower gold number indicates a higher protective power.

Step 4: Creating Ordered List by Protective Power

Order the colloids by their protective power (from highest to lowest): - Colloid D: 0.005 - Colloid B: 0.01 - Colloid C: 0.10 - Colloid A: 0.50.

Step 5: Finding Correct Option

Compare the calculated order (D > B > C > A) with the given options to find a match. The order matches option (c).

Key Concepts

Gold Number

The gold number of a colloid provides a quantitative measure of its ability to prevent the coagulation of a gold sol. Imagine you have a suspension of gold particles in water. These particles tend to clump together and settle at the bottom. By adding a small amount of a protective colloid, you can keep the particles dispersed and stable.

So, what is a gold number? It represents the minimum amount (in milligrams) of the protective colloid required to stop 10 mL of a standard gold sol from turning blue or red, which indicates coagulation. Essentially:

• A lower gold number means stronger protective power because less colloid is needed.
• A higher gold number indicates weaker protective power since more colloid is required.

Knowing the gold number helps chemists choose the right colloid for various applications to maintain the stability of suspensions.

Protective Colloid

A protective colloid is a substance that prevents particles in a colloidal system from coagulating. These substances help maintain the stability and uniformity of colloidal particles within a dispersion.

When you add a protective colloid to a system, it adsorbs onto the surface of the particles, providing a barrier. This makes it harder for particles to come close enough to stick together and settle. Protective colloids are important in:

• Food production, to stabilize textures.
• Pharmaceuticals, to keep active ingredients evenly distributed.
• Paints and inks, to ensure even color mixing.

These colloids often include proteins, synthetic polymers, or certain gums and starches. Their effectiveness is directly related to their structure and chemical composition, impacting how they interact with the particles.

Protective Power

Protective power refers to the effectiveness of a protective colloid in preventing the coagulation of another colloid in a suspension. It is closely linked to the gold number but represents the ability to keep particles stable on a practical level.

If a colloid has high protective power, it will require only a small amount to achieve stability. This term is especially useful when comparing different colloids and determining which will provide the best protection in different scenarios.

• High protective power means stronger stabilization effects.
• Low protective power indicates that more of the colloid is needed to achieve the same stabilization.

In colloidal chemistry, picking a colloid with the right protective power is crucial for creating stable emulsions or suspensions, enabling longer shelf life and consistent performance.

Colloidal Stability

Colloidal stability is the condition where particles in a colloidal system remain evenly distributed without settling or clumping over time. Maintaining this stability is key for various industrial and scientific applications, as it determines the product's performance and longevity.

Stable colloids exhibit minimal particle aggregation, which can otherwise lead to settling and separation if not properly controlled. Factors affecting colloidal stability include:

• Particle size and distribution.
• The presence of additives like protective colloids.
• The ionic strength and pH of the surrounding medium.

Understanding and controlling these factors allows for the designing of mixtures with desirable properties, from appealing food textures to efficient drug delivery systems.