Question

In the coagulation of a positive sol, the flocculating power of the ions \(PO_4^{3-}\), \(SO_4^{2-}\) and \(Cl^-\) decreases in the order

• A. \(PO_4^{3-} > Cl^- > SO_4^{2-}\)
• B. \(PO_4^{3-} > SO_4^{2-} > Cl^-\)
• C. \(Cl^- > SO_4^{2-} > PO_4^{3-}\)
• D. \(Cl^- > PO_4^{3-} > SO_4^{2-}\)
• E. \(SO_4^{2-} > PO_4^{3-} > Cl^-\)

Hint:

For coagulation, higher valency of the oppositely charged ion means greater flocculating power.

Answer 1

The Correct Option is B

Concept: According to Hardy-Schulze rule, the coagulating power of an ion increases with its charge. For a positive sol, anions cause coagulation.

Step 1: Identify counter ions.
Positive sol is coagulated by negative ions: \[ PO_4^{3-},\ SO_4^{2-},\ Cl^- \]

Step 2: Compare charges.
\[ PO_4^{3-} \text{ has charge } -3 \] \[ SO_4^{2-} \text{ has charge } -2 \] \[ Cl^- \text{ has charge } -1 \]

Step 3: Apply Hardy-Schulze rule.
Higher charge means higher flocculating power: \[ PO_4^{3-} > SO_4^{2-} > Cl^- \]