Question

Which of the following statement(s) is/are true about negatively charged sol?

• A. Coagulation in sol can be brought about by persistent dialysis
• B. Coagulation in sol can be brought about by addition of electrolytes
• C. $K_{2}S{O}_4$ solution coagulates the sol more readily than $MgC{l}_2$
• D. Trace amount of electrolyte in solution gives stability to sol

Answer 1

Answer: (A), (B), (D)

Trace amount of electrolyte in solution gives stability to sol

Methods for preparing coagulation of lyophobic sol:

(i) By persistent dialysis:
Trace amount of electrolyte in solution gives stability to sol. If traces of the electrolyte present in the sol are removed completely, the sol becomes unstable and ultimately coagulate.

(ii) By addition of electrolytes:
When excess of an electrolyte is added, the colloidal particles are precipitated. This is due to the interaction of colloids with ions carrying opposite charge. These ions are called coagulating ions.

Here, the given sol is negatively charge so it interact with positive ions. When $K_{2}S{O}_4$ or $MgC{l}_2$ are added to sol, the sol react with positive ions of the electrolyte.
By Hardy-Schulze rule, greater the valence of flocculating/coagulating ion added, greater is its power to cause coagulation.

Hence, $MgC{l}_2$ solution coagulates the sol more readily than $K_{2}S{O}_4$ due to +2 charge on $Mg$.

Therefore, statements (a), (b) and (d) are true.