Which of the following electrolyte will have maximum flocculation value for Fe(OH)₃ sol?

NaCl

The correct answer is option 1. NaCl.

Out of the listed options, \(NaCl\) (sodium chloride) will have the maximum flocculation value for \(Fe(OH)_3\) (ferric hydroxide) sol. Here's why:

Flocculation and Hardy-Schulze Rule:

Flocculation refers to the process of coagulation (particle aggregation) and precipitation of colloidal particles. When an electrolyte is added to a colloid, it can destabilize the colloid and cause flocculation.

The Hardy-Schulze rule helps predict the effectiveness of electrolytes in causing flocculation. It states that the effectiveness of an electrolyte in causing flocculation increases with the valence (charge) of the ion with the opposite sign of the charge on the colloidal particle.

\(Fe(OH)_3\) Sol and Electrolytes:

\(Fe(OH)_3\) sol is positively charged due to the adsorption of positive ions (like \(Fe^{3+}\) or \(OH^+\)) on the surface of the particles. Among the listed electrolytes:

\(NaCl (Na^+Cl^-)\) has a monovalent anion \((Cl^-)\).

\(Na^2S (2Na^+ S^{2-})\) has a divalent anion \((S^{2-})\).

\((NH_4)_3PO_4 (3NH_4^+ PO_4^{3-})\) has a trivalent anion \((PO_4^{3-})\).

\(K_2SO_4 (2K^+ SO_4^{2-})\) has a divalent anion \((SO_4^{2-})\).

According to the Hardy-Schulze rule, since \(Fe(OH)_3\) sol is positively charged, an anion (negatively charged ion) will be more effective in causing flocculation. Out of the options, chloride ion \((Cl^-)\) in \(NaCl\) has the lowest valence \((1)\). A lower valence ion disrupts the electrostatic stabilization of the colloid less effectively compared to a higher valence ion. Therefore, \(NaCl\) will require a higher concentration (higher flocculation value) to cause flocculation compared to electrolytes with divalent or trivalent anions.

\(NaCl\), having the lowest charged anion \((Cl^-)\) among the given options, will require the highest concentration to cause flocculation in \(Fe(OH)_3\) sol. This translates to \(NaCl\) having the maximum flocculation value for \(Fe(OH)_3\) sol.