Question

Which of the following electrolytes 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:

For coagulation of colloids, remember the Hardy–Schulze rule: The ion with charge opposite to the colloidal particles and having the highest valency causes maximum coagulation.

Answer 1

The Correct Option is C

Concept: According to the Hardy–Schulze rule, the coagulating power of an electrolyte depends on the valency of the ion having charge opposite to that of the colloidal particles.
• For a negative sol, the cation is responsible for coagulation.
• Higher the valency of the cation, greater will be its coagulating power.

Step 1: Identify the charge on the sol. The sol \(As_2S_3\) is a negatively charged sol. Therefore, the coagulating ion must be a cation.

Step 2: Compare the valency of cations in the given electrolytes. \[ NaCl \rightarrow Na^+ \quad (\text{valency } = 1) \] \[ MgCl_2 \rightarrow Mg^{2+} \quad (\text{valency } = 2) \] \[ AlCl_3 \rightarrow Al^{3+} \quad (\text{valency } = 3) \]

Step 3: Apply Hardy–Schulze rule. \[ Al^{3+} > Mg^{2+} > Na^+ \] Thus, \(Al^{3+}\) has the highest coagulating power. \[ \boxed{AlCl_3} \]