Question

The coagulating power of electrolytes having ions Na$^+$, Al$^{3+}$ and Ba$^{2+}$ for As$_2$S$_3$ sol increases in the order

• A. Al$^{3+}$ $<$ Ba$^{2+}$ $<$ Na$^{+}$
• B. Na$^{+}$ $<$ Ba$^{2+}$ $<$ Al$^{3+}$
• C. Ba$^{2+}$ $<$ Na$^{+}$ $<$ Al$^{3+}$
• D. Al$^{3+}$ $<$ Na$^{+}$ $<$ Ba$^{2+}$

Hint:

Using a simple frame or just bolding for the box
Key Points: 
As$_2$S$_3$ sol is negatively charged. 
Coagulation of negatively charged sols is caused by cations. 
Hardy-Schulze Rule: Coagulating power increases significantly with increasing charge magnitude of the coagulating ion. 
Cation Charges: Na$^{+}$ (+1), Ba$^{2+}$ (+2), Al$^{3+}$ (+3). 
Increasing Coagulating Power: Na$^{+}$ $<$ Ba$^{2+}$ $<$ Al$^{3+}$.

Answer 1

The Correct Option is B

The coagulation (or flocculation) of a colloidal sol involves neutralizing the charge on particles, leading to aggregation and precipitation. (A) As₂S₃ Sol: Arsenic sulfide (As₂S₃) sol, a negatively charged colloid, typically gains its negative charge from sulfide ions (S^2-) adsorbed onto As₂S₃ particles. (B) Coagulation with Electrolytes: To coagulate a negatively charged sol, add electrolytes with positively charged ions (cations). Cations neutralize the negative charge on sol particles. (C) Hardy-Schulze Rule: This rule states that an ion's effectiveness in causing coagulation (coagulating power) correlates directly with the magnitude of its charge. For a negatively charged sol, a cation's coagulating power increases with its positive charge. (D) Comparing Ions: We have the cations Na⁺, Ba²⁺, and Al³⁺, with charges of +1, +2, and +3, respectively. (E) Order of Coagulating Power: Based on the Hardy-Schulze rule, coagulating power follows the charge magnitude order: Al³⁺>Ba²⁺>Na⁺ (F) Increasing Order: The question asks for the order of *increasing* coagulating power. Therefore, order the ions from lowest to highest coagulating power: Na⁺<Ba²⁺<Al³⁺ This matches option (B).