Question

Which electrolyte is most effective in the coagulation of a negative sol like \(As_2S_3\)?

• A. \(NaCl\)
• B. \(MgCl_2\)
• C. \(AlCl_3\)
• D. \(KCl\)

Hint:

Hardy–Schulze rule: Higher valency of the counter-ion → greater coagulation power. For negative sols, cations are responsible for coagulation.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The coagulation of a colloidal solution depends on the valency of the active ion (the ion carrying a charge opposite to that of the sol particles).
Step 2: Key Formula or Approach:
Hardy-Schulze Rule: The greater the valency of the flocculating ion, the greater is its power to cause precipitation.
Step 3: Detailed Explanation:
Since \(As_2S_3\) is a negatively charged sol, it requires a positively charged ion (cation) for coagulation. Comparing the cations in the given electrolytes:
\(Na^+\) (from \(NaCl\)) - Valency 1
\(Mg^{2+}\) (from \(MgCl_2\)) - Valency 2
\(Al^{3+}\) (from \(AlCl_3\)) - Valency 3
\(K^+\) (from \(KCl\)) - Valency 1
According to the Hardy-Schulze rule, \(Al^{3+}\) has the highest valency and therefore the highest coagulating power.
Step 4: Final Answer:
\(AlCl_3\) is the most effective electrolyte.