Question

The coagulating power of electrolytes having ions $Na^+, Al^{3+}$ and $Ba^{2+}$ for arsenic sulphide sol increases in the order

• A. $Al^{3+} < Ba^{2+} < Na^+$
• B. $Na^+ < Ba^{2+} < Al^{3+}$
• C. $Ba^{2+} < Na^{2+} < Al^{3+}$
• D. $Al^{3+} < Na^+ < Ba^{2+}$

Answer 1

The Correct Option is B

The problem at hand requires understanding the coagulating power of various electrolytes for arsenic sulphide sol. The coagulating power of an electrolyte is determined using the Schulze-Hardy rule, which states that the greater the valency of the active ion (opposite charge to that of the colloidal particles), the more effective it is in coagulating the colloid. 

Arsenic sulphide sol is a negatively charged sol. Therefore, the ions that will affect coagulation positively are cations. Given the cations \(Na^+\), \(Ba^{2+}\), and \(Al^{3+}\), let's determine their coagulating power:

1. Sodium Ion (\(Na^+\)): This ion has a valency of 1. Although it can cause coagulation, its power is the weakest among the three ions listed because of the lowest charge.
2. Barium Ion (\(Ba^{2+}\)): This ion has a higher valency of 2, thereby stronger coagulating power than \(Na^+\) due to its higher charge.
3. Aluminium Ion (\(Al^{3+}\)): This ion has the highest valency of 3. According to the Schulze-Hardy rule, it will have the highest coagulating power among the given ions.

Therefore, the order of coagulating power of these ions for arsenic sulphide sol is:

\(Na^+ < Ba^{2+} < Al^{3+}\)

This corresponds to the correct answer option:

 

\(Na^+ < Ba^{2+} < Al^{3+}\)