Question

The most effective coagulating agent for antimony sulphide sol is

• A. \(\text{Na}_2\text{SO}_4\)
• B. \(\text{CaCl}_2\)
• C. \(\text{NH}_4\text{Cl}\)
• D. \(\text{Al}_2(\text{SO}_4)_3\)

Hint:

Flocculation value \(\propto \frac{1}{(\text{Valency})^6}\). A small increase in valency dramatically increases coagulating power. For negative sol: \(\text{Al}^{3+}>\text{Ba}^{2+}>\text{Na}^+\).

Answer 1

The Correct Option is D

Step 1: Determine Charge of Sol:
Antimony sulphide (\(\text{Sb}_2\text{S}_3\)) is a metal sulphide sol, which are generally negatively charged.
Step 2: Apply Hardy-Schulze Rule:
The rule states: 1. The effective ion for coagulation is the one carrying a charge opposite to that of the sol particles. (Here, we need cations). 2. Higher the valency of the flocculating ion (coagulating ion), greater is its power to cause coagulation.
Step 3: Analyze Options:
We need the cation with the highest positive charge. (A) \(\text{Na}_2\text{SO}_4 \rightarrow \text{Na}^+\) (Charge +1) (B) \(\text{CaCl}_2 \rightarrow \text{Ca}^{2+}\) (Charge +2) (C) \(\text{NH}_4\text{Cl} \rightarrow \text{NH}_4^+\) (Charge +1) (D) \(\text{Al}_2(\text{SO}_4)_3 \rightarrow \text{Al}^{3+}\) (Charge +3) Since \(\text{Al}^{3+}\) has the highest valency (+3), Aluminum sulphate is the most effective coagulating agent. Final Answer:
Option (D).