Problem 56 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Consider the following list of reagents: [Adv. 2014] Acidified \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\), alkaline \(\mathrm{KMnO}_{4}, \mathrm{CuSO}_{4}, \mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{Cl}_{2}, \mathrm{O}_{3}, \mathrm{FeCl}_{3}, \mathrm{HNO}_{3}\) and \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) The total number of reagents that can oxidise aqueous iodide to iodine is

Step-by-Step Solution

Answer

7 reagents can oxidize iodide to iodine.

Step 1: Identify the Role of Reagents

To determine which reagents can oxidize aqueous iodide (I⁻) to iodine (I₂), we first need to understand their oxidative properties. An oxidizing agent can accept electrons and be reduced in the process, hence causing the oxidation of another substance, in this case, iodide ions.

Step 2: Analyze Acidified Potassium Dichromate ( K_2Cr_2O_7 )

Acidified K_2Cr_2O_7 is a strong oxidizing agent. It is known to oxidize iodide ( I^- ) ions to iodine ( I_2 ). So, it can oxidize aqueous iodide to iodine.

Step 3: Analyze Alkaline Potassium Permanganate ( KMnO_4 )

Alkaline KMnO_4 is also a strong oxidizing agent. In alkaline conditions, permanganate ions ( MnO_4^- ) can oxidize iodide to iodine. Thus, alkaline KMnO_4 can oxidize aqueous iodide to iodine.

Step 4: Analyze Copper(II) Sulfate ( CuSO_4 )

CuSO_4 is not a strong enough oxidizing agent to oxidize iodide ions to iodine in typical reactions. Hence, it does not oxidize aqueous iodide to iodine.

Step 5: Analyze Hydrogen Peroxide ( H_2O_2 )

H_2O_2 acts as an oxidizing agent under acidic conditions and can oxidize iodide ions to iodine. Therefore, H_2O_2 can be used to oxidize aqueous iodide to iodine.

Step 6: Analyze Chlorine ( Cl_2 )

Chlorine is a strong oxidizing agent and can oxidize iodide ions to iodine. Therefore, Cl_2 can oxidize aqueous iodide to iodine.

Step 7: Analyze Ozone ( O_3 )

Ozone is a powerful oxidizing agent and can oxidize iodide ions to iodine. Thus, O_3 can oxidize aqueous iodide to iodine.

Step 8: Analyze Ferric Chloride ( FeCl_3 )

FeCl_3 is a moderate oxidizing agent that can oxidize iodide ions to iodine. Thus, FeCl_3 can oxidize aqueous iodide to iodine.

Step 9: Analyze Nitric Acid ( HNO_3 )

HNO_3 is a strong oxidizing agent, especially in concentrated form, and can oxidize iodide ions to iodine. Thus, HNO_3 can oxidize aqueous iodide to iodine.

Step 10: Analyze Sodium Thiosulfate ( Na_2S_2O_3 )

Na_2S_2O_3 is not an oxidizing agent; it actually reduces iodine to iodide. Therefore, it cannot oxidize iodide ions to iodine.

Step 11: Count All Applicable Reagents

Add up all the reagents that can oxidize iodide to iodine: K_2Cr_2O_7 , KMnO_4 , H_2O_2 , Cl_2 , O_3 , FeCl_3 , and HNO_3 . This gives us a total of 7 reagents.

Key Concepts

Oxidizing Agents

An oxidizing agent is a substance that has the ability to accept electrons from another species during a chemical reaction. This electron acceptance results in the oxidizing agent being reduced while the other substance is oxidized. In simpler terms, oxidizing agents help convert one substance into another by taking away its electrons. In the context of the JEE Chemistry exercise, various reagents were evaluated for their ability to oxidize iodide ions ( I^- ) to iodine ( I_2 ).
Oxidizing agents are widely used in various chemical reactions and processes, including:

• Bleaching: Used in the whitening of paper and textiles.
• Disinfecting: Commonly used to kill bacteria and viruses in water purification systems.
• Energy production: Utilized in batteries and other chemical processes to generate electricity.

Understanding how different oxidizing agents work is crucial in both industrial applications and laboratory practices, making this a significant topic for students preparing for exams like JEE Advanced Chemistry.

Iodide to Iodine Oxidation

In chemical terms, the oxidation of iodide ions (I^- ) to iodine (I_2 ) involves the loss of electrons by the iodide ions. This is a classic example of an oxidation reaction, which is a fundamental concept in redox (reduction-oxidation) chemistry.
During this specific reaction, iodide ions lose electrons, which are subsequently gained by the oxidizing agent present in the reaction. The transformation can be written as:\[2I^- \rightarrow I_2 + 2e^-\]Different reagents have different affinities and capabilities to oxidize iodide ions. Some common reagents capable of this oxidation, as discussed in JEE Advanced Chemistry 2014, include acidified potassium dichromate (K_2Cr_2O_7 ), alkaline potassium permanganate (KMnO_4 ), hydrogen peroxide (H_2O_2 ), and chlorine (Cl_2 ). Each of these reagents can effectively perform this oxidative conversion under suitable conditions, allowing the conversion of I^- to I_2 in various chemical settings.

JEE Advanced Chemistry 2014

The JEE Advanced Chemistry exam is known for challenging aspiring engineers with its in-depth and comprehensive questions. In 2014, the exam presented students with an exercise involving the identification of oxidizing agents capable of converting aqueous iodide to iodine. This test examined both theoretical understanding and practical application of redox chemistry concepts.
Excelling in such exams requires a strong grasp of chemistry fundamentals, including understanding chemical bonding, thermodynamics, equilibria, and kinetics in addition to reactions involving oxidizing agents. Students must be well-versed with reagent properties, their uses, and the conditions favoring their action, as evidenced by their ability to determine the appropriate reagents for specific oxidations such as iodide to iodine.
Preparing for JEE Advanced Chemistry challenges students to hone their skills in problem-solving, critical thinking, and conceptual understanding. It's essential for students to practice various problems, refer to authoritative study materials, and engage with interactive learning experiences to achieve success in exams like the JEE.