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

As₂S₃ sol is a negatively charged colloid. According to the Hardy-Schulze rule, the coagulating power of an electrolyte is directly proportional to the valency of the ions carrying the charge opposite to that of the sol particles. Therefore, a positively charged ion with a higher valency will be more effective in coagulating the As₂S₃ sol.

Let's analyze each option:

• CaCO₃: Provides Ca²⁺ ions, which are positively charged with a valency of +2.
• NaCl: Provides Na⁺ ions, which are positively charged with a valency of +1.
• FeCl₃: Provides Fe³⁺ ions, which are positively charged with a valency of +3.
• Clay: Clay particles are generally negatively charged and hence won't cause coagulation.

Among the given options, Fe³⁺ ions from FeCl₃ have the highest positive charge (+3). Therefore, FeCl₃ will be the most effective coagulating agent for As₂S₃ sol.

Therefore, the correct answer is FeCl₃.