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

Step 1: Understanding the Question:
The question relates to the coagulation (precipitation) of colloidal solutions by the addition of electrolytes.
Step 2: Key Formula or Approach:
The Hardy-Schulze Rule states:
1. Coagulation is caused by ions having a charge opposite to that of the colloidal particles.
2. The greater the valency of the flocculating ion, the greater is its power to cause coagulation.
Step 3: Detailed Explanation:
The given sol \( As_2S_3 \) (Arsenious sulphide) is a negative sol.
To coagulate a negative sol, we need cations (positively charged ions).
Let's look at the cations provided by the options:
(A) \( NaCl \rightarrow Na^+ \) (Valency = +1)
(B) \( MgCl_2 \rightarrow Mg^{2+} \) (Valency = +2)
(C) \( AlCl_3 \rightarrow Al^{3+} \) (Valency = +3)
(D) \( KCl \rightarrow K^+ \) (Valency = +1)
According to the rule, higher the charge, higher the effectiveness.
Since \( Al^{3+} \) has the highest charge among the choices, it will be the most effective.
Step 4: Final Answer:
\( AlCl_3 \) is the most effective electrolyte because it provides the trivalent \( Al^{3+} \) ion.