Question

For \( \text{As}_2\text{S}_3 \) sol, the most effective coagulating agent is:

• A. \( \text{CaCO}_3 \)
• B. \( \text{NaCl} \)
• C. \( \text{FeCl}_3 \)
• D. \( Clay \)

Hint:

The coagulation efficiency increases with the charge of the ion, following the Hardy-Schulze rule, which states that higher charges cause more effective coagulation.

Answer 1

The Correct Option is C

Arsenic trisulfide (As₂S₃) sol is a negatively charged colloid. The Hardy-Schulze rule states that the coagulating power of an electrolyte is directly proportional to the charge magnitude of the ion carrying the opposite charge to the sol particles. Consequently, a cation with a higher positive charge will more effectively coagulate As₂S₃ sol.

Analysis of each option:

• CaCO₃: Dissociates to yield Ca²⁺ ions (positive charge, valency +2).
• NaCl: Dissociates to yield Na⁺ ions (positive charge, valency +1).
• FeCl₃: Dissociates to yield Fe³⁺ ions (positive charge, valency +3).
• Clay: Clay particles are typically negatively charged and thus ineffective for coagulation.

Comparing the options, Fe³⁺ ions from FeCl₃ possess the highest positive charge (+3). Therefore, FeCl₃ is the most potent coagulating agent for As₂S₃ sol.

The correct choice is FeCl₃.