Problem 113 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements are correct? (1) The smaller the gold number of a lyophilic colloid, the larger will be its protective power. (2) Lyophilic sols in contrast to lyophobic sols, are easily coagulated on addition of small amounts of electrolytes. (3) Ferric chloride solution is used to stop bleeding from a fresh cut because it coagulates blood. (4) The flocculation value of arsenious sulphide sol is independent of the anion of the coagulating electrolyte. Select the correct answer using the codes given below: (a) 1,2 and 4 (b) 1,2 and 3 (c) 1,3 and 4 (d) 2,3 and 4

Step-by-Step Solution

Answer

The correct answer is (c) 1, 3, and 4.

Step 1: Understand Gold Number and Protective Power

The gold number of a colloid is the minimum amount in milligrams needed to prevent coagulation of a 10 ml gold sol by 1 ml of 10% NaCl. A smaller gold number means the colloid has a higher protective power because less material is needed to prevent coagulation. Therefore, statement (1) is correct.

Step 2: Compare Lyophilic and Lyophobic Colloids

Lyophilic colloids are more stable than lyophobic colloids and require more electrolyte to coagulate. Therefore, they are not easily coagulated by small amounts of electrolytes. Thus, statement (2) is incorrect.

Step 3: Assess the Role of Ferric Chloride in Blood Coagulation

Ferric chloride can coagulate proteins in blood, thus stopping bleeding from a fresh cut. Therefore, statement (3) is correct.

Step 4: Evaluate Flocculation Values with Anion Type

The flocculation value of a colloid depends on the type and charge of ions in the electrolyte, particularly the anions. Therefore, statement (4) is incorrect, as the flocculation value depends on the anion of the coagulating electrolyte.

Step 5: Determine Correct Statements

From steps 1 to 4, statements (1) and (3) are correct. So the correct combination of statements is (c): 1, 3, and 4.

Key Concepts

Gold Number

The term "Gold Number" might sound a bit shiny, but in chemistry, it has a unique significance. It measures the protective power of a colloid, especially with lyophilic colloids. Essentially, it refers to the minimum amount of a protective colloid needed in milligrams to prevent the coagulation of a standard gold sol under specific conditions. Confusing as it may appear, the smaller the gold number, the better the protective efficiency of the colloid.

To break it down further:

• A smaller gold number indicates a more effective protective colloid, as less of it is needed to stabilize the colloid.
• This concept emphasizes the efficiency or stability of the colloid in preventing coagulation.
• In practical scenarios, this means a gold number of 5 is more protective than a gold number of 10.

Lyophilic Colloids

Lyophilic colloids also known as "solvent-loving" colloids, have a natural affinity for the solvent, which makes them highly stable. Such colloids are easy to form because of the strong interaction between the dispersed particles and the dispersion medium.

Key characteristics of lyophilic colloids include:

• These colloids are reversible, which means they can re-form if the dispersion medium is removed and then added again.
• Unlike lyophobic colloids, they require a substantial amount of electrolytes for coagulation.
• These can include substances like gelatin, starch, or gum, which naturally attract water.

This unique property makes lyophilic colloids less prone to coagulation compared to their counterparts, lyophobic colloids.

Coagulation of Blood

The coagulation of blood is a crucial biological process that prevents excessive bleeding when we're injured. It is often compared to forming a blood clot over an open wound to "plug the leak". Chemical agents like ferric chloride can accelerate this process, making them useful in controlling bleeding.

Here’s how it works:

• Ferric chloride helps by interacting with proteins in the blood.
• Its effectiveness is largely due to its ability to induce protein coagulation.
• This leads to the thickening of blood at the site of the wound and promptly stops the bleeding.

Understanding how certain chemicals interact with blood displays the principle behind medical uses of chemistry, especially in situations where quick coagulation is desired.

Flocculation Value

Understanding flocculation is key to understanding how colloids become stable or unstable. Flocculation value is the minimum concentration of an electrolyte needed to cause the flocculation of a colloid. This value is not constant and varies depending on the ions present in the electrolyte.

Important aspects related to flocculation value:

• Generally correlated with the type and charge of the ions rather than specific compounds.
• This highlights the role of anions in controlling the stability of colloids.
• For example, ions with higher charge densities tend to be more effective at causing flocculation.

Recognizing how various ions influence the flocculation value of a colloid aids in understanding processes within countless industrial applications and natural phenomena.