Question

Which of the following is reduced by hydrogen peroxide in acid medium? (a) \(\mathrm{FeSO}_{4}\) (b) Potassium iodide (c) Potassium ferrocyanide (d) Potassium permanganate

Short answer

Potassium permanganate (Option d) is reduced by hydrogen peroxide in acid medium.

Step-by-step solution

Identify the Reducing Agent

In this problem, hydrogen peroxide ( H_2O_2) is acting as a reducing agent in an acidic medium. A reducing agent donates electrons to another substance, meaning H_2O_2 will cause another compound to gain electrons.

Determine the Likely Oxidants

We need to assess which of the given compounds can accept electrons (be reduced). Consider the oxidation properties of: (a) FeSO_4, (b) KI, (c) K_4[ Fe( CN)_6], (d) KMnO_4.

Reduction Potential Consideration

Potassium permanganate ( KMnO_4) in acidic medium is a well-known strong oxidizing agent, meaning it accepts electrons and gets reduced to Mn^{2+} or MnO_2.

Conclusion

Comparing the known properties, KMnO_4 (Option (d)) is most likely to be reduced by hydrogen peroxide in acidic medium. It accepts electrons, gets reduced, and changes its oxidation state during the reaction.

Key concepts

Reducing Agents

In the realm of chemistry, reducing agents are substances that donate electrons to another compound in a chemical reaction. Imagine a reducing agent as a generous friend who freely gives away its things - electrons in this context - to another needy friend. When a reducing agent donates electrons, it causes the other substance—the oxidizing agent—to gain electrons and undergo a reduction. Hence, the reducing agent itself gets oxidized in the process.
In our specific exercise, hydrogen peroxide ( H_2O_2) acts as a reducing agent in an acidic medium. It's like a helper that enables the compounds it reacts with to gain electrons and be reduced in a reaction. This special capability of donating electrons allows hydrogen peroxide to play a crucial role in chemical reactions, especially in redox reactions. Hydrogen peroxide in an acidic environment is a versatile player that can shift between roles as it reacts with different substances.

Oxidizing Agents

Oxidizing agents are the other side of the coin in redox reactions. While reducing agents donate electrons, oxidizing agents are the compounds that accept these electrons. Picture them as receivers who fill up their electron needs from generous donors such as reducing agents. These agents play a role in oxidizing other substances by taking in electrons, which leads to a reduction in the oxidizing agent’s own state.
In an acidic medium, a classic example of an oxidizing agent is potassium permanganate ( KMnO_4). With its distinctive purple color, potassium permanganate is a powerful oxidizer which can accept multiple electrons from reducing agents, thereby turning into manganese ions, specifically Mn^{2+} or MnO_2. This capacity to undergo a change in oxidation state by accepting electrons is how KMnO_4 becomes reduced in a reaction with hydrogen peroxide, showcasing its essential role as an oxidizing agent.

Acidic Medium Reactions

Reactions in an acidic medium are unique environments where redox chemistry often thrives. Here, the presence of acids creates a medium that can significantly alter and sometimes accelerate the reaction process. When a solution is acidic, it means that it has a higher concentration of protons ( H^+) available, which can influence the behavior and outcome of the chemical reactions taking place.
In our exercise, hydrogen peroxide reacts in an acidic medium, which can enhance its reducing capabilities. An acidic environment aids in improving the electron transfer processes by providing extra H^+ ions. This is particularly important when dealing with substances like potassium permanganate because the presence of an acidic medium can help to stabilize the intermediate states these agents pass through during the reaction.
By utilizing an acidic medium, the reactions become more efficient, and the reducing and oxidizing processes become more pronounced, enabling substantive changes in the chemical states of the substances involved. This property makes acidic solutions a popular choice for conducting controlled redox processes in laboratory and industrial settings.