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

Short answer

The correct answer is (c) 1 and 3.

Step-by-step solution

Understanding Statement 1

Statement (1) claims that the smaller the gold number of a lyophilic colloid, the larger its protective power. The gold number is a measure of a colloid's capacity to prevent the coagulation of a lyophobic sol by electrolytes. A lower gold number indicates higher protective power. Therefore, statement (1) is correct.

Evaluating Statement 2

Statement (2) asserts that lyophilic sols are easily coagulated by small amounts of electrolytes compared to lyophobic sols. In reality, lyophilic sols are more stable in the presence of electrolytes because they form hydrogen bonds or have van der Waals interactions, whereas lyophobic sols are less stable and more easily coagulated by electrolytes. Therefore, statement (2) is incorrect.

Analyzing Statement 3

Statement (3) suggests that ferric chloride is used to stop bleeding because it coagulates blood. Ferric chloride acts as a coagulant and is effective in coagulating blood proteins, thus helping to stop bleeding. Therefore, statement (3) is correct.

Examining Statement 4

Statement (4) claims that the flocculation value of arsenious sulphide sol is independent of the anion of the coagulating electrolyte. This is false because flocculation value, which is the concentration of an electrolyte needed to coagulate a sol, depends on the valency and nature of the anion in the electrolyte due to Schulze-Hardy rule. Therefore, statement (4) is incorrect.

Selecting the Correct Answer

Based on the evaluations, statements (1) and (3) are correct. Therefore, the correct answer is (c) 1, 3 and 4.

Key concepts

Gold Number

The gold number is a significant concept in colloidal chemistry, especially when dealing with lyophilic colloids. It is a quantitative measure of how effective a protective colloid is in preventing the coagulation of a lyophobic colloid by an electrolyte. The smaller the gold number, the more effective the protective colloid is. This means it requires less of the lyophilic colloid to prevent coagulation.

Some important points about the gold number include:

• A lower gold number means higher protective power.
• The gold number is determined experimentally.
• It plays a critical role in scenarios where the stability of colloidal systems is essential, such as in certain industrial and biomedical applications.

Understanding this concept is crucial for effectively utilizing colloids in various chemical processes.

Lyophilic Colloids

Lyophilic colloids, also known as hydrophilic colloids when the medium is water, are colloidal systems that are naturally stable. A key factor in this stability is their affinity for the dispersion medium, which allows them to form hydrogen bonds or engage in van der Waals forces.

Here are some notable characteristics of lyophilic colloids:

• They are more resistant to coagulation even when electrolytes are added.
• Tends to be reversible, meaning they can be re-dispersed in the medium after precipitation.
• Examples include proteins, starch, and gelatin.

Lyophilic colloids are contrasted with lyophobic colloids, which lack such a natural affinity for the medium and are more prone to coagulation.

Coagulation

Coagulation is a process where dispersed colloidal particles aggregate to form larger particles, leading to the eventual settling out of the particles from the suspension. This process is often induced by the addition of electrolytes.

Some critical points about coagulation:

• Often accompanies the loss of charge that keeps colloidal particles suspended.
• Electrolytes neutralize the charges, leading to particle aggregation.
• In practical applications, coagulation is used in water treatment and in the medical field to stop bleeding, such as with ferric chloride.

Understanding coagulation aids in the control and manipulation of colloids in both industrial and biological systems.

Flocculation Value

The flocculation value pertains to the concentration of electrolytes necessary to precipitate or coagulate a colloid. It is directly linked to the nature of the ions in the electrolyte, especially the valence of the anion as per the Schulze-Hardy rule.

Here are some key aspects of flocculation value:

• Higher valency of an anion decreases the flocculation value, meaning less electrolyte is needed for coagulation.
• The specific type of electrolyte and its ions affects the effectiveness in coagulation.
• Understanding flocculation values helps in designing effective formulations in processes such as wastewater treatment.

Notably, the flocculation value helps predict how different electrolytes will interact with colloids, essential for many chemical applications.