Question

A colloidal solution is subjected to an electric field. The colloidal particles move toward the anode. In the coagulation of this solution using NaCl, BaCl2, and AlCl3 separately, which one is the correct order of coagulation power?

• A. NaCl \textgreater BaCl2 \textgreater AlCl3
• B. BaCl2 \textgreater AlCl3 \textgreater NaCl
• C. NaCl \textgreater AlCl3 \textgreater BaCl2
• D. AlCl3 \textgreater BaCl2 \textgreater NaCl

Hint:

Coagulation power increases with the charge of the ion; trivalent ions have the highest coagulation power.

Answer 1

The Correct Option is D

Step 1: Understanding coagulation power.
Coagulation power refers to the ability of an electrolyte to cause the aggregation or clumping of colloidal particles. The coagulation power increases with the valency of the ions and the charge they carry. Step 2: Comparing the electrolytes.
- \( \text{NaCl} \) provides Na+ ions, which are monovalent. - \( \text{BaCl}_2 \) provides Ba2+ ions, which are divalent. - \( \text{AlCl}_3 \) provides Al3+ ions, which are trivalent. Since the coagulation power increases with the charge of the ion, AlCl3 has the highest coagulation power, followed by BaCl2, and finally NaCl. Step 3: Conclusion.
The correct order of coagulation power is (4) AlCl3 \textgreater BaCl2 \textgreater NaCl.

Answer 2

This question is about the Hardy-Schulze rule for coagulation of a negatively charged sol (the particles move to the anode, so they carry a negative charge and need cations to neutralize them). Let's assess each option by comparing the cation valencies involved.

1. NaCl \( \textgreater \) BaCl2 \( \textgreater \) AlCl3: This places the monovalent Na\(^+\) electrolyte as the strongest coagulant, which is backwards - Hardy-Schulze states coagulating power INCREASES, not decreases, with cation charge.
2. BaCl2 \( \textgreater \) AlCl3 \( \textgreater \) NaCl: This correctly puts NaCl last, but wrongly ranks the divalent Ba\(^{2+}\) electrolyte above the trivalent Al\(^{3+}\) electrolyte, when a higher charge should give greater, not lesser, coagulating power.
3. NaCl \( \textgreater \) AlCl3 \( \textgreater \) BaCl2: This again starts with the weakest coagulant (monovalent Na\(^+\)) at the top, which contradicts the rule.
4. AlCl3 \( \textgreater \) BaCl2 \( \textgreater \) NaCl: Al\(^{3+}\) is trivalent, Ba\(^{2+}\) is divalent, and Na\(^+\) is monovalent. Since the negative sol needs cations to neutralize its charge, and coagulating power rises sharply with cation valency (roughly as the 6th power of charge per the Hardy-Schulze rule), the trivalent ion is the most effective, followed by the divalent ion, with the monovalent ion the weakest.

The only order that ranks the cations by increasing charge from weakest to strongest coagulant is AlCl3 \( \textgreater \) BaCl2 \( \textgreater \) NaCl.

Therefore, the correct answer is AlCl3 \( \textgreater \) BaCl2 \( \textgreater \) NaCl.