Question

$Fe(OH)_3$ sol can be more easily coagulated by $Na_3PO_4$ in comparison to $KCl$ because

• A. mass of $Na_3PO_4$ is more than $KCl$ hence it is more effective than $KCl$
• B. phosphate ion $(PO_4^{3-})$ has higher negative charge than $Cl^-$ ion hence are more effective for coagulation
• C. $KCl$ is more soluble than $Na_3PO_4$ hence less effective for coagulation
• D. $Na^+$ ions are more effective than $K^+$ ions for coagulation.

Answer 1

Answer: (B)

Ferric hydroxide is a positively charged sol hence ions carrying negative charge can coagulate it. Since $PO_4^{3-}$ has higher negative charge than $Cl^-$ hence it is more effective for coagulation.