Question

Which out of the following electrolyte solutions having the same concentration will be most effective in causing the coagulation of arsenic sulfide sol?
a.) KCl
b.) ${ MgCl }_{ 2 }$
c.) ${ AlCl }_{ 3 }$
d.) ${ Na }_{ 3 }{ PO }_{ 4 }$

Answer 1

Hint: Coagulation is a process of aggregating together the colloidal particles so as to change them into large-sized particles which ultimately settle as a precipitate. Another name for coagulation is precipitation. Coagulation is generally brought by the addition of electrolyte.

Complete answer:
The coagulation capacity of different electrolytes is different. It depends upon the valency of the active ion called a flocculating ion, which is the ion carrying charge opposite to the charge on the colloidal particles.
Hardy Schulze rule: “As per this rule, more prominent the valency of the active ion or flocculating particle, more noteworthy will be its coagulating power”.
Thus, Hardy Schulze law state:
(i) The ions carrying the charge opposite to that of sol particles are effective in causing a coagulation of the sol.
(ii) The coagulating intensity of an electrolyte is legitimately relative to the valency of the active ion (particles causing coagulation).
Arsenic sulfide is a negative sol, so we have to utilize a positive sol for its coagulation.
Here, the valency of the accessible sols are ${ { K }^{ + }{ ,Na }^{ + },Al }^{ +3 }{ ,Mg }^{ +2 }$
In this way, ${ Al }^{ +3 }$ has the greatest valency, and hence it will coagulate arsenic sulfide sol more.
So, the correct answer is “Option C”.

Note: The possibility to make a mistake is that in Hardy Schulze rule, it depends on the flocculating value. The process of accumulating the colloidal particles together to transform them into large sized particles which at last settles as precipitate is called flocculation.