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

Question

Standard reduction electrode potentials of three metals \(\mathrm{A}, \mathrm{B}\) and \(\mathrm{C}\) are \(+0.5 \mathrm{~V},-3.0 \mathrm{~V}\) and \(-1.2 \mathrm{~V}\) respectively. The reducing power of these metals are [2003] (a) \(\mathrm{B}>\mathrm{C}>\mathrm{A}\) (b) \(\mathrm{A}>\mathrm{B}>\mathrm{C}\) (c) \(\mathrm{C}>\mathrm{B}>\mathrm{A}\) (d) \(\mathrm{A}>\mathrm{C}>\mathrm{B}\)

Step-by-Step Solution

Answer

(a) B > C > A

Step 1: Understanding Reduction Potentials

The standard reduction potential indicates a substance's tendency to gain electrons, thus getting reduced. A higher reduction potential means the substance is a better oxidizing agent and prefers to be reduced.

Step 2: Interpreting Given Values

We are given the reduction potentials: - Metal A: +0.5 V - Metal B: -3.0 V - Metal C: -1.2 V From these values, Metal A has the highest and Metal B has the lowest reduction potential.

Step 3: Relation to Reducing Power

The lower the reduction potential, the stronger the reducing agent. Therefore, reducing power is inversely related to the reduction potential value.

Step 4: Assessing Reducing Power

Based on the potentials: - Metal B with -3.0 V has the highest reducing power. - Metal C with -1.2 V has the second highest reducing power. - Metal A with +0.5 V has the lowest reducing power.

Step 5: Identifying Correct Order

The reducing power of the metals in decreasing order is: Metal B > Metal C > Metal A.

Step 6: Choose Correct Option

Based on our analysis, the correct answer is option (a) \( B > C > A \).

Key Concepts

Reduction Potential

Reduction potential, often mentioned in electrochemistry, refers to a substance's tendency to gain electrons. This potential is measured in volts and indicates how easily a species is reduced. The higher the reduction potential, the more likely the substance will gain electrons and undergo the reduction process. This also means the substance functions as an oxidizing agent. For example, if Metal A has a reduction potential of +0.5 V, it demonstrates a greater tendency to accept electrons compared to a metal with a lower reduction potential. Reduction potentials are vital for predicting the direction of redox reactions. When comparing two substances, the one with the higher reduction potential will act as the oxidizing agent, while the other species will be reduced. Generally, in a redox couple:

• If substance X has a higher reduction potential than Y, then X is reduced, and Y is oxidized.
• In practical applications, this concept helps determine the feasibility and spontaneity of reactions.

Reducing Agent

A reducing agent is a substance that donates electrons to another species, causing the latter to be reduced. In the process, the reducing agent itself gets oxidized. The power of a reducing agent is determined by its ability to lose electrons easily. The key to understanding reducing agents lies in reduction potentials:

• Metals with low (or more negative) reduction potentials are strong reducing agents.
• Such metals readily lose electrons and encourage the reduction of other species.

For instance, in our exercise, Metal B with a reduction potential of -3.0 V is a strong reducing agent compared to Metal A with +0.5 V, as the lower reduction potential indicates a greater electron donation capability. Knowing which metal acts as an effective reducing agent can guide you in predicting reactions and designing batteries or electrochemical cells.

Electrochemistry Concepts

Electrochemistry primarily deals with the relationships between electrical energy and chemical changes. The fundamental concepts include:

• Oxidation and Reduction Reactions: These are the chemical processes where electrons are transferred between species. Oxidation involves the loss of electrons, while reduction involves the gain of electrons.
• Electrode Potentials: These are potentials developed by substances when they either lose or gain electrons. This potential difference drives the flow of electrons in a circuit.
• Galvanic Cells: These are devices that convert chemical energy into electrical energy through spontaneous redox reactions.

Electrochemistry finds extensive applications in areas such as corrosion prevention, battery technology, and electroplating. Understanding these concepts equips students to predict reaction outcomes, devise efficient systems, and analyze the activity of various metals.

Metal Activity Series

The metal activity series is a list that ranks metals by their reactivity. It's a valuable tool that chemists use to predict the outcomes of single-replacement reactions, where a more reactive metal displaces a less reactive one from a compound. The series arranges metals from the highest to the lowest reactivity:

• Higher ranked metals: These have strong tendencies to lose electrons, making them good reducing agents. They typically have more negative or lower reduction potentials.
• Lower ranked metals: These are less likely to lose electrons and often cannot displace metals that are higher in the series.

In our example, Metal B, with its low reduction potential, would be high on the activity series, while Metal A would be lower due to its higher reduction potential. Using this series helps in predicting whether a particular metal will successfully undergo a redox reaction with another metal, aiding in problem-solving and real-world applications.