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

Correct Statements: 1 and 3 only, no precise option available.

Step 1: Understanding Statement 1

According to the gold number among lyophilic colloids, a smaller gold number indicates a higher protective power of the colloid. This statement is true. The protective power reflects the capacity to stabilize other colloids, with a lower number indicating a better protective effectiveness.

Step 2: Analyzing Statement 2

Lyophilic sols are more stable than lyophobic sols and require larger amounts of electrolytes to coagulate. Therefore, Statement 2 is false as it states the opposite—that they are easily coagulated by small amounts of electrolytes.

Step 3: Reviewing Statement 3

When blood coagulation is required, ferric chloride can be applied to expose cuts since it helps blood proteins to coagulate, creating a barrier that stops the bleeding. Therefore, Statement 3 is correct.

Step 4: Evaluating Statement 4

The flocculation value of arsenious sulphide sol is dependent on the properties of the electrolyte anion involved, contrary to the statement. Thus, Statement 4 is false as the flocculation value is not independent of the anion.

Step 5: Selecting the Correct Statements

Based on the evaluations: Statements 1 and 3 are correct. Neither Option (c) nor any option offers just these two as correct choices. Only option that pairs 1 and 3 along with additional false statements correctly pairs two true statements, (b) Statements 1, 2, and 3. However, option (b) includes a false statement (2) implying there is an oversight. Correct answer should only include actual correct statements.

Key Concepts

Lyophilic Colloids

Lyophilic colloids are a fascinating group of colloidal systems where the dispersing medium has a strong affinity for the dispersed phase. This means that the colloid particles are "liquid-loving," or lyophilic, in nature. One of the key features of lyophilic colloids is their stability.

These colloids are quite stable because the dispersed phase is well-solvated or coated by the dispersion medium, forming a protective layer around the particles. This stability means that lyophilic colloids don’t easily aggregate or coagulate. However, when managing such colloids, it's important to understand the concept of the gold number, which indicates a lyophilic colloid's protective power.

The gold number is a quantitative measure. A lower gold number signifies higher protective power, meaning the colloid is better at preventing other colloids from aggregating. In practical terms, lyophilic colloids can be used to stabilize less stable lyophobic colloids, enhancing their resistance to coagulation when electrolytes are present. They do this by surrounding the particles of the lyophobic colloid with their well-hydrated shells, making it difficult for ions to reach the lyophobic particles.

Lyophobic Sols

Lyophobic sols are opposite to lyophilic colloids in that they do not have an affinity for the liquid in which they are dispersed. "Lyophobic" means "solvent-hating." These colloids are characterized by their significant instability.

Because lyophobic sols are not stabilized by a solvation layer like lyophilic colloids, they are more prone to coagulate or form aggregates when even small amounts of electrolytes are added. Without sufficient protective layers, the particles in lyophobic sols can attract and stick to one another, forming larger aggregates that settle out of the dispersion.

This sensitive behavior towards electrolytes makes lyophobic sols important when considering reactions and processes that require sensitive manipulations at the colloidal level. Their nature gives them unique properties, useful in applications where rapid coagulation is required, simply by introducing specific ions or changing physical conditions.

Coagulation in Chemistry

Coagulation is a fundamental chemical process where particle dispersion is reduced, leading to aggregation and settling from a solution. It plays a crucial role in many natural and industrial processes.

Coagulation is especially relevant in systems involving colloids. In particular, when discussing blood coagulation, a fascinating example is the use of ferric chloride. On application to a cut, ferric chloride induces the coagulation of blood proteins, helping form a clot to stop bleeding. This chemical approach showcases a controlled application of coagulation for therapeutic purposes.

Beyond medical applications, coagulation is vital in water treatment, paint formulation, and food production. Different coagulants and conditions can be tailored to target specific colloidal systems, depending on the desired results. In essence, controlling coagulation by manipulating electrolytes and environmental conditions is crucial in managing systems where colloidal stability or instability is essential.