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

Concept: According to the Hardy–Schulze rule: The greater the valency of the ion responsible for neutralizing the charge of a colloidal particle, the greater its coagulating power. For a negatively charged sol, the coagulating ions are positive ions (cations).

Step 1: Identify the nature of the sol. The sol \(As_2S_3\) is a negative sol. Thus, cations will cause coagulation.

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

Step 3: Apply Hardy–Schulze rule. Since the coagulating power increases with valency: \[ Al^{3+} > Mg^{2+} > Na^+ = K^+ \]

Step 4: Identify the most effective electrolyte. Thus the most effective coagulating electrolyte is: \[ AlCl_3 \]