Question

Which of the following is reduced by hydrogen peroxide in acidic medium? (a) ferrous sulphate (b) potassium iodide (c) potassium ferrocyanide (d) potassium permanganate

Short answer

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

Step-by-step solution

Analyze the Reaction Conditions

We are given that the reaction takes place in an acidic medium. In such a medium, hydrogen peroxide acts as an oxidizing agent. We need to find which of the given substances can be reduced by hydrogen peroxide.

Understand the Reducing Properties

In acidic medium, hydrogen peroxide can reduce strong oxidizing agents. Thus, the substances that are typically reduced are those which have higher oxidation states and can accept electrons.

Evaluate Each Option

- (a) **Ferrous sulphate (FeSO₄):** contains Fe²⁺, which is usually oxidized to Fe³⁺, not reduced. - (b) **Potassium iodide (KI):** contains I⁻, which can be oxidized to I₂. - (c) **Potassium ferrocyanide ( ext{K}_4[ ext{Fe}( ext{CN})_6]):** the Fe here is in a stable low oxidation state (+2) and does not commonly participate in reduction. - (d) **Potassium permanganate (KMnO₄):** contains Mn in a high oxidation state (+7) and thus can be reduced to lower oxidation states.

Identify the Correct Answer

Hydrogen peroxide can reduce potassium permanganate (KMnO₄), where Mn has a high oxidation state and can easily accept electrons to be reduced to Mn²⁺ or other lower oxidation states.

Key concepts

Hydrogen Peroxide

Hydrogen peroxide, or H₂O₂, is a common chemical substance with the formula H₂O₂. It's known for its disinfectant properties, but it plays a fascinating role in chemical reactions as well.
In chemistry, hydrogen peroxide is famous for its dual role as both an oxidizing and reducing agent, depending on the conditions. This property allows it to participate in various reaction types. When used in acidic mediums, as in our exercise scenario, hydrogen peroxide acts as an oxidizing agent.

• It has the potential to accept electrons from other substances, oxidizing them.
• This versatility makes H₂O₂ a key player in numerous chemical processes.

Its role as an oxidizing agent is crucial in reduction reactions, where it helps to transform the oxidation states of other substances. In environments with specific stability conditions, it can either give or take electrons, usually leading to simpler, more manageable products.

Acidic Medium Reactions

In the context of chemical reactions, the medium plays a significant role in determining the behavior of reactants. An acidic medium provides protons (H⁺ ions), which can facilitate or influence the direction and outcome of a reaction.

• Hydrogen peroxide in an acidic solution becomes more effective as an oxidizing agent.
• It can cause other compounds to lose electrons more readily.

For the chemical given in our exercise question, an acidic medium enhances the ability of hydrogen peroxide to reduce agents that are in high oxidation states.
This characteristic is essential for reactions where electron transfer is involved, such as those with potassium permanganate. It's important to understand the impact of pH on reaction mechanisms and outcomes, as it dictates the efficiency and selectivity of the reactions involved.

Oxidation States

The concept of oxidation states is central to understanding redox reactions. Oxidation states indicate the degree of oxidation of an atom in a substance.
Basically, it shows how many electrons an atom has gained, lost, or shared during its chemical bonding.

• An increase in oxidation state corresponds to oxidation, while a decrease indicates reduction.
• Substances in high oxidation states, like Mn in potassium permanganate (Mn +7), are prime candidates for reduction.

The exercise focuses on finding which substance hydrogen peroxide can reduce in an acidic medium. By analyzing the oxidation states, you can predict which substances are easily reduced. Potassium permanganate, for instance, undergoes reduction when it interacts with reducing agents, forming manganese ions in lower oxidation states, like Mn²⁺. Understanding oxidation states allows us to pinpoint feasible reactions and balance chemical equations accurately.

Chemical Reduction

Reduction is one half of a redox reaction, the process by which a substance gains electrons. In the miscellaneous world of chemistry, reduction often comes with oxidation, forming what we call redox reactions.
Chemical reduction involves a decrease in oxidation state and is often facilitated by reducing agents. These agents either lose electrons themselves or donate them, thus reducing another substance.

• In the exercise, hydrogen peroxide acts as the oxidizing agent, thereby reducing potassium permanganate.
• The Mn in KMnO₄, known for its high oxidation state, accepts electrons and transforms to a lower oxidation state like Mn⁺² in acidic conditions.

This transformation highlights the nature of reduction, where electron transfer dictates the change. Recognizing the potential for chemical reduction in reactions helps us decipher complex chemical behaviors, predict reaction products, and apply this understanding in practical chemical processes.