Question

Which of the following exhibits greater coagulation power towards a negative colloid?

• A. $Z n S O_{4}$
• B. $N a_{3}P O_{4}$
• C. $A l C l_{3}$
• D. $K_{4}\left[F e \left(C N\right)_{6}\right]$

Answer 1

Answer: (C)

Negative colloid is coagulated by positive ion or vice-versa. Greater the valency of coagulating ion, greater will be coagulating power according to Hardy-Schulze rule.
$\left(\text{a}\right) \, \, \left(\text{ZnSO}\right)_{4} \rightarrow \left(\text{Zn}\right)^{2 +} + \text{SO}_{4}^{2 -}$
$\left(\text{b}\right) \, \, \left(\text{Na}\right)_{3} \left(\text{PO}\right)_{4} \rightarrow 3 \left(\text{Na}\right)^{+} + \text{PO}_{4}^{3 -}$
$\left(\text{c}\right) \, \, \left(\text{AlCl}\right)_{3} \rightarrow \left(\text{Al}\right)^{3 +} + 3 \left(\text{Cl}\right)^{-}$
$\left(\text{d}\right) \, \, \left(\text{K}\right)_{4} \left[\text{Fe} \left(\text{CN}\right)_{6}\right] \rightarrow 4 \left(\text{K}\right)^{+} + \left(\left[\text{Fe} \left(\text{CN}\right)_{6}\right]\right)^{4 -}$
Since, in $A l C l_{3}$ , the valency of positive ion (coagulation ion) is highest, it is the most powerful coagulating agent among the given to coagulate the negative colloid.