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

The coagulation of a negatively charged sol, such as \( \text{As}_2\text{S}_3 \), is most effective with a highly positively charged ion, according to the Hardy-Schulze rule.
Among the given options:
\( \text{FeCl}_3 \) dissociates to produce \( \text{Fe}^{3+} \), which has the highest positive charge (\( +3 \)).
Higher positive charges effectively neutralize the negative charge of the sol, leading to coagulation.
In contrast, \( \text{CaCO}_3 \) (which produces \( \text{Ca}^{2+} \)) and \( \text{NaCl} \) (which produces \( \text{Na}^+ \)) are less effective because their ions have lower positive charges.
Final Answer: \[ \boxed{\text{FeCl}_3} \]