Problem 182 - A Complete Resource Book in Chemistry for JEE Main

Question

Standard reduction electrode potentials of three metals A, B and \(C\) are \(+0.5 \mathrm{~V},-3.0 \mathrm{~V}\) and \(-1.2 \mathrm{~V}\) respectively. The reducing power of these metals are (a) \(\mathrm{B}>\mathrm{C}>\mathrm{A}\) (b) \(A>B>C\) (c) \(C>B>A\) (d) \(\mathrm{A}>\mathrm{C}>\mathrm{B}\)

Step-by-Step Solution

Answer

(a) B > C > A

Step 1: Understanding Electrode Potentials

The standard reduction electrode potential indicates the tendency of a species to gain electrons. A more positive potential means a stronger tendency to gain electrons, making the species a better oxidizing agent. Conversely, a more negative potential implies a stronger tendency to lose electrons and act as a reducing agent.

Step 2: Arranging Potentials

The electrode potentials provided are: for A, +0.5 V; for B, -3.0 V; and for C, -1.2 V. Arrange these potentials from most negative to most positive: -3.0 V (B), -1.2 V (C), +0.5 V (A).

Step 3: Determining Reducing Power

The reducing power of a metal is inversely related to its electrode potential. The more negative the potential, the stronger its reducing power. Hence, metal B, with the most negative potential, has the strongest reducing power, followed by metal C, and then metal A.

Step 4: Selecting the Correct Order

From the arrangement, B has the most significant reducing power, followed by C, and then A. Therefore, the correct order of reducing power is B > C > A.

Key Concepts

Standard Reduction Potential

Standard reduction potential is a key concept in electrochemistry. It tells us how easily a chemical species can gain electrons. This is crucial to understand because gaining electrons is what characterizes a substance's ability to act as an oxidizing agent.

When we look at the standard reduction potentials of metals, like in our example with metals A, B, and C, we focus on their values:

• A has a potential of +0.5 V.
• B has a potential of -3.0 V.
• C has a potential of -1.2 V.

A positive potential, like metal A’s +0.5 V, indicates a good oxidizing agent because it shows a tendency to attract electrons.

In contrast, negative potentials, observed in metals like B and C, suggest that these metals readily lose electrons, thus serving as better reducing agents. So, the more negative the value, the less likely the substance is to gain electrons, making it a better reductant.

Reducing Agent

Reducing agents are substances that donate electrons during chemical reactions. By doing so, they become oxidized themselves. In other words, a good reducing agent is one that easily loses electrons. This is critical in understanding redox reactions where such agents reduce another molecule while getting oxidized.

In our problem, the reducing power of a metal is related to its standard reduction potential:

• A lower, more negative potential means a higher tendency to lose electrons.
• Metal B, with its -3.0 V, has the strongest reducing power among the three metals.
• C comes next with its potential of -1.2 V, and finally, A with +0.5 V has the least reducing power.

Therefore, the order of reducing power is B > C > A, because B has the most negative electrode potential, proving its ability to release electrons more readily compared to C and A.

Oxidizing Agent

An oxidizing agent is a substance that gains electrons in a chemical reaction and, by doing so, oxidizes another substance. This means that it gets reduced itself. The strength of an oxidizing agent is normally inversely related to its reducing power.

The standard reduction potential helps us understand the oxidizing nature of a substance. Simply put,

• A higher, more positive standard reduction potential indicates a strong oxidizing agent.
• Metal A, with a potential of +0.5 V, is the strongest oxidizing agent among the three because it has the highest potential to gain electrons.
• Metals B and C, with negative reduction potentials, are weaker oxidizing agents but stronger reducing agents.

This clarity allows us to determine that, between our three metals, A is the best at acting as an oxidizing agent and attracting electrons into its structure.