Problem 81 - A Complete Resource Book in Chemistry for JEE Main

Question

The product formed on oxidation of \(\mathrm{I}^{-}\)with \(\mathrm{MnO}_{4}\) - in alkaline medium is (a) \(\mathrm{IO}_{4}^{-}\) (b) \(\mathrm{I}_{2}\) (c) IO (d) \(\mathrm{IO}_{3}^{-}\)

Step-by-Step Solution

Answer

The product is \( \mathrm{IO}_{3}^{-} \).

Step 1: Identify Reaction Participants

The reaction involves the oxidation of iodide ions \( \mathrm{I}^{-} \) by permanganate ions \( \mathrm{MnO}_{4}^{-} \) in an alkaline medium. We need to determine which iodine species forms as a result.

Step 2: Oxidizing Agent in Alkaline Medium

In an alkaline medium, permanganate \( \mathrm{MnO}_{4}^{-} \) is known to oxidize \( \mathrm{I}^{-} \) to higher oxidation states of iodine. We have to determine which iodine oxide or oxyanion is stable under these conditions.

Step 3: Evaluate Possible Products

Examine the possible iodine products: \( \mathrm{IO}_{4}^{-} \), \( \mathrm{I}_{2} \), \( \mathrm{IO} \), and \( \mathrm{IO}_{3}^{-} \). In alkaline media, the end oxidation product for \( \mathrm{I}^{-} \) often leads to an oxyanion, such as \( \mathrm{IO}_{3}^{-} \) and not \( \mathrm{IO}_{4}^{-} \), since \( \mathrm{IO}_{4}^{-} \) formation requires a stronger oxidizing environment.

Step 4: Conclusion

Based on the known behavior of permanganate in alkaline conditions and typical oxidation states for iodine, \( \mathrm{IO}_{3}^{-} \) is the most feasible oxidation product.

Key Concepts

Iodine oxides

Iodine oxides are compounds formed by the reaction of iodine with oxygen. These compounds can have different oxidation states depending on the conditions of the reaction. In the context of alkaline medium reactions, iodine often forms oxyanions, which are ionic forms where iodine is bonded to oxygen. Here are some key points about iodine oxides:

• Variety of Oxidation States: Iodine can exist in several oxidation states in oxides, ranging from +1 to +7. However, in alkaline conditions, the more stable and common oxidation state is +5, forming iodate (\( \mathrm{IO}_{3}^{-} \)).


• Iodates vs. Periodates: Iodates (\( \mathrm{IO}_{3}^{-} \)) are typically more stable in alkaline conditions than periodates (\( \mathrm{IO}_{4}^{-} \)), which require much stronger oxidizing conditions to form.


• Applications: Iodine oxides, particularly iodates, are used in chemical reactions and various industrial processes, including water purification and as a chemical intermediate.

Understanding the formation and stability of iodine oxides is critical for correctly anticipating the products in redox reactions like the one described in this exercise.

Permanganate ions

Permanganate ions (\( \mathrm{MnO}_{4}^{-} \)) are well-known oxidizing agents in chemistry, particularly effective in acidic and alkaline media. These ions are derived from manganese in its highest oxidation state, +7, which enables them to accept electrons readily during redox reactions. Some important characteristics of permanganate ions include:

• Color and Redox Properties: The permanganate ion is distinctly purple and is a powerful oxidizing agent. It can undergo reduction, leading to various products depending on the medium it reacts in.


• Behavior in Different Media: In alkaline solutions, permanganate ions reduce to manganese dioxide (\( \mathrm{MnO}_{2} \)) rather than manganese (IV) salts, which are common in acidic conditions.


• Common Applications: Permanganate is frequently used in titrations, organic synthesis, and water treatment for oxidizing organic impurities.

In the given reaction with iodide ions, permanganate's role is to transfer its high oxidation potential to convert \( \mathrm{I}^{-} \) to \( \mathrm{IO}_{3}^{-} \). Understanding the specific role and behavior of permanganate ions helps to correctly predict reaction outcomes.

Alkaline medium oxidation

An alkaline medium, characterized by a high pH, influences the behavior and products of redox reactions. The presence of hydroxide ions (\( \mathrm{OH}^{-} \)) can significantly alter both the mechanism and the products of oxidation reactions. In the case of iodine oxidation by permanganate ions, alkaline conditions favor the formation of particular iodine species:

• Product Stability: Under alkaline conditions, iodine molecules are more likely to form iodate (\( \mathrm{IO}_{3}^{-} \)) rather than periodate due to the stabilization of lower oxidation states by hydroxide ions.


• Enhanced Oxidation: Alkaline media can increase the oxidizing potential of certain agents, promoting the oxidation of different substrates to more stable products.


• Mechanism Influence: Hydroxide ions might participate in the formation and stabilization of oxyanions, affecting the course of the reaction by shifting the equilibrium towards more stabilized forms.

The alkaline medium's effect on reaction pathways is a key aspect for students to consider when analyzing oxidation reactions, ensuring a deeper comprehension of chemical interactions and product formation.