Concept Explanation: Oxidizing Agents for Iodide to Iodine

Iodide ions (I⁻) can be oxidized to iodine (I₂) by various oxidizing agents. The reaction is:

$2I^{-}\to I_2+2e^{-}$

Any reagent with a higher reduction potential than iodine (E° for I₂/I⁻ is +0.54 V) can oxidize iodide to iodine. We will evaluate each reagent step by step.

Step-by-Step Evaluation:

Step 1: Acidified K₂Cr₂O₇ - It is a strong oxidizing agent (E° = +1.33 V). It oxidizes I⁻ to I₂.

Step 2: Alkaline KMnO₄ - In alkaline medium, it can oxidize I⁻ to I₂, though it might further oxidize to iodate in hot conditions. But generally, it does oxidize to I₂.

Step 3: CuSO₄ - Copper(II) ions oxidize I⁻ to I₂ (E° for Cu²⁺/Cu⁺ is +0.15 V, but reaction occurs due to low solubility of CuI).

Step 4: H₂O₂ - It oxidizes I⁻ to I₂ in acidic medium.

Step 5: Cl₂ - Chlorine is a stronger oxidizing agent (E° = +1.36 V) and oxidizes I⁻ to I₂.

Step 6: O₃ - Ozone is a powerful oxidizing agent and oxidizes I⁻ to I₂.

Step 7: FeCl₃ - Iron(III) oxidizes I⁻ to I₂ (E° for Fe³⁺/Fe²⁺ is +0.77 V).

Step 8: HNO₃ - Nitric acid oxidizes I⁻ to I₂.

Step 9: Na₂S₂O₃ - Sodium thiosulfate is not an oxidizing agent; it reduces I₂ to I⁻ (used in iodometric titrations). It does not oxidize iodide.

Final Answer: The reagents that can oxidize aqueous iodide to iodine are: Acidified K₂Cr₂O₇, alkaline KMnO₄, CuSO₄, H₂O₂, Cl₂, O₃, FeCl₃, and HNO₃. Na₂S₂O₃ cannot. Thus, the total number is 8.

Related Topics:

• Oxidation-Reduction Reactions
• Standard Electrode Potentials
• Properties of Halogens and Halides
• Iodometric Titrations

Important Formulae and Theory:

The standard reduction potential (E°) determines the strength of oxidizing agents. An oxidizing agent with E° greater than +0.54 V can oxidize I⁻ to I₂.

General reaction: $2I^{-}\to I_2+2e^{-}$

Example with Fe³⁺: $2{\mathrm{Fe}}^{3+}+2I^{-}\to 2{\mathrm{Fe}}^{2+}+I_2$