Question

$Fe(OH{)}_3$ sol can be more easily coagulated by $N{a}_{3}P{O}_4$ in comparison to $KCl$ because:

• A. Mass of $N{a}_{3}P{O}_4$ is more than $KCl$ hence it is more effective than $KCl$
• B. Phospate ion $\left(P{O}^{3-}\right)$ has higher negative charge than $C{l}^{-}$ ion
• C. $KCl$ is more soluble than $N{a}_{3}P{O}_4$ hence less effective for coagulation
• D. $N{a}^{+}$ ions are more effective than $K^{+}$ ions for coagulation

Answer 1

The correct option is B Phospate ion $\left(P{O}^{3-}\right)$ has higher negative charge than $C{l}^{-}$ ion

Hardy-Schulze Rule:
Greater the valence of flocculating ion added, greater is its power to cause coagulation.

Coagulating power of bivalent ion is 20-80 times higher than monovalent ion. Coagulating power of trivalent ion is many more times higher than divalent ion.

$Fe(OH{)}_3$ is a positive sol so it is coagulated by a negative ion.
Here, phospate ion $P{O}^{3-}$ has higher negative charge than $C{l}^{-}$ ion. Hence by Hardy-Schulze rule phospate ion is more effective for coagulation of $Fe(OH{)}_3$