Question

A colloidal solution is subjected to an electric field than colloidal particles more towards anode. The amount of electrolytes of BaCl₂, AlCl₃ and NaCl required to coagulate the given colloid is in the order

• A. NaCl > BaCl₂ > AlCl₃
• B. BaCl₂ < AlCl₃ > NaCl
• C. AlCl₃ = NaCl = BaCl₂
• D. AlCl₃ > BaCl₂ > NaCl

Answer 1

The Correct Option is A

1. Understand the Hardy-Schulze Rule
The Hardy-Schulze rule states that the coagulating power of an electrolyte is directly proportional to the valency of the ions carrying the charge opposite to that of the colloidal solution. In simpler terms, the greater the charge on the ion that neutralizes the colloid, the more effective it is at causing coagulation. This means that a smaller amount of the electrolyte with the higher charge is needed for coagulation.

2. Determine the charge of the colloidal particles
The question states that "colloidal particles move more towards the anode." This implies that the colloidal particles are negatively charged since they are attracted to the positive electrode (anode).

3. Identify the effective ions for coagulation
Since the colloidal particles are negatively charged, the positive ions (cations) of the electrolytes will be effective in causing coagulation. The electrolytes are:

- NaCl → $Na^+$ + $Cl^-$ (cation is $Na^+$ with a +1 charge)
- $BaCl_2$ → $Ba^{2+}$ + $2Cl^-$ (cation is $Ba^{2+}$ with a +2 charge)
- $AlCl_3$ → $Al^{3+}$ + $3Cl^-$ (cation is $Al^{3+}$ with a +3 charge)

4. Apply the Hardy-Schulze Rule to determine the order of coagulating power
According to the Hardy-Schulze rule, the coagulating power increases with the charge of the cation. Therefore, the order of coagulating power is:

$Al^{3+}$ > $Ba^{2+}$ > $Na^+$

Since the question asks for "The amount of electrolytes... required to coagulate the given colloid," we need to consider that the amount of electrolyte needed will be inversely proportional to the coagulating power. That is, the higher the charge of the ion, the LESS of the electrolyte needed. Thus, the amount required will be in the opposite order.

Therefore, the order of the amount of electrolyte required is:

NaCl > $BaCl_2$ > $AlCl_3$

5. Compare with the given options
Comparing the derived order with the options, we find that it matches option (A).

Final Answer:
(A) NaCl > $BaCl_2$ > $AlCl_3$

Answer 2

Coagulation of a colloidal solution depends on the electrolyte’s ability to neutralize the charge on colloidal particles. The more the valency of the cation, the more efficient the electrolyte is in coagulating the colloid.

The order of coagulation power is:

• NaCl has a single positive ion (Na⁺) and is least efficient in coagulation.
• BaCl₂ has a divalent cation (Ba²⁺) and is more efficient than NaCl.
• AlCl₃ has a trivalent cation (Al³⁺) and is the most efficient at coagulating the colloidal particles.

Thus, the order of coagulation is NaCl > BaCl₂ > AlCl₃.

So, the correct answer is (A): NaCl > BaCl₂ > AlCl₃.