Question

Which of the following electrolytes is the least effective in causing coagulation of colloidal solution of ferric hydroxide?

• A. KBr
• B. K$_2$SO$_4$
• C. K$_2$CrO$_4$
• D. K$_3$[Fe(CN)$_6$]

Hint:

Electrolytes with high charge density are more effective at coagulating colloidal solutions due to their ability to neutralize the charges on colloidal particles.

Answer 1

The Correct Option is A

Step 1: Understand coagulation of colloidal solutions.
The process of coagulation involves the addition of an electrolyte to a colloidal solution, which neutralizes the charges on the colloidal particles, causing them to aggregate and settle. The effectiveness of coagulation depends on the charge and the size of the ion.
Step 2: Analyze the options.
- KBr (Option A) is the least effective because bromide ions are smaller and have lower charge density, making them less effective at neutralizing the charge of the colloidal particles. - K$_2$SO$_4$ (Option B) contains larger sulfate ions that are more effective at coagulating the colloidal solution. - K$_2$CrO$_4$ (Option C) also has larger ions with a higher charge density. - K$_3$[Fe(CN)$_6$] (Option D) is the most effective, as the hexacyanoferrate ions are highly charged, leading to strong coagulation effects.
Step 3: Apply to the options.
The correct answer is (A) KBr.
Final Answer: \[ \boxed{\text{KBr}} \]