Question

Arsenic (Ill) sulphide forms a sol with a negative charge. Which of the following ionic substances should be most effective in coagulating the sol?

• A. $KCl$
• B. $MgC{l}_2$
• C. $A{l}_2(S{O}_4{)}_3$
• D. $N{a}_{3}P{O}_4$

Answer 1

The correct option is C $A{l}_2(S{O}_4{)}_3$

To coagulate negative sol of $A{s}_2{S}_3$, the coagulation power of different cations decrease in the order $A{l}^{3+}>M{g}^{2+}>K^{+}>N{a}^{+}$
hence, the floculation value increases in the order $A{l}^{3+}<M{g}^{2+}<K^{+}<N{a}^{+}$
The flocculating values (in milli moles/litre) of $A{l}^{3+}>M{g}^{2+}>K^{+}>N{a}^{+}$ are 0.093, 0.72, 50 and 51 respectively.
Thus, $A{l}_2(S{O}_4{)}_3$ is the most effective in coagulating the sol.