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 \mathrm{\\{} o r d e r ~ o f ~ t h e i r ~ p r o t e c t i v e ~ p o w e r s ~ i s ~ (a) \(\mathrm{D}<\mathrm{A}<\mathrm{C}<\mathrm{B}\) (b) \(C

Step-by-Step Solution

Answer

Option (c): \(\mathrm{A}<\mathrm{C}<\mathrm{B}<\mathrm{D}\) is correct.

Step 1: Understanding Gold Number

The gold number is a measure of the protective power of colloids. It represents the minimum amount (in milligrams) of protective colloid required to prevent the coagulation of 10 ml of gold sol by 1 ml of a 10% sodium chloride solution. A smaller gold number indicates a higher protective power.

Step 2: Identify Gold Numbers

Given the gold numbers: - A: 0.50 - B: 0.01 - C: 0.10 - D: 0.005 These are the gold numbers for the colloids A, B, C, and D, respectively.

Step 3: Determine Protective Power Order

The protective power is inversely proportional to the gold number. Therefore, a lower gold number means a higher protective power. To list these in order from highest protective power to lowest, we arrange them by increasing gold numbers: - D: 0.005 - B: 0.01 - C: 0.10 - A: 0.50

Step 4: Match With Given Options

From the determined order, we match the protective power order (highest to lowest): 1. D2. B3. C4. AThis corresponds to the option (c): \(\mathrm{A}<\mathrm{C}<\mathrm{B}<\mathrm{D}\).

Key Concepts

Gold Number

The gold number is an important concept in understanding colloidal systems. It refers to the minimum amount of a protective colloid needed to stop a colloidal gold solution from coagulating when a salt is added. Basically, if we're dealing with a gold sol mixed with sodium chloride, the gold number tells us how much colloid is needed to keep it stable.

A lower gold number signifies greater protective power because it means less colloid is needed to guard against coagulation. For example, if Colloid C has a gold number of 0.10, this means that 0.10 mg of C is needed to protect the gold sol. Comparing gold numbers like 0.50 or 0.01 helps us rank colloids by their protection effectiveness: the smaller the number, the more efficient the colloid.

Coagulation Prevention

Coagulation prevention is about maintaining the stability of colloids so they don't clump together and settle out of a solution. When these particles come together, or 'coagulate', it can cause issues in various applications where maintaining a uniform mixture is vital.

Protective colloids play a key role in this, as they can stabilize the solution by preventing coagulation. They provide a barrier around colloidal particles, thus reducing the chance of them coming together when salts like sodium chloride are added. A small amount of protective colloid that can effectively prevent coagulation speaks to its high stability-inducing capability.

Protective Colloids

Protective colloids are substances that stabilize other colloidal particles in a suspension by forming a protective layer around them. This layer hinders the particles from sticking together, thus maintaining the uniform distribution of the colloid in the suspension.

They are crucial in many industrial and scientific applications where uniform particle dispersion is crucial. Colloids like gelatin, gum arabic, and albumin are typical examples used in various industries, from food production to pharmaceuticals. By measuring the gold number, you can determine how much of a particular colloid you need to effectively prevent coagulation, ensuring the colloid remains stable.