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: Understand Electrode Potential

The standard reduction electrode potential indicates the tendency of a species to gain electrons and be reduced. For a metal, the more negative the standard reduction potential, the better reducing agent it is, because it indicates a greater tendency to lose electrons.

Step 2: Compare Reduction Potentials

The given standard reduction potentials are: \( A = +0.5 \text{ V} \), \( B = -3.0 \text{ V} \), and \( C = -1.2 \text{ V} \). To determine reducing power, we compare these values: \( B \) has the most negative electrode potential, followed by \( C \), and then \( A \) with the least negative (most positive) potential.

Step 3: Determine Reducing Power Order

Since reducing power is greater for metals with more negative reduction potentials, the order of reducing power is \( B > C > A \). \( B \), with \(-3.0\text{ V}\), is the strongest reducing agent, while \( A \), with \(+0.5\text{ V}\), is the weakest.

Key Concepts

Standard Reduction Potential

The standard reduction potential is a crucial concept in electrochemistry. It measures how readily a species gains electrons – in other words, how easily it gets reduced. Each element or compound has a specific standard reduction potential value, expressed in volts (V). A more positive potential indicates a stronger tendency to gain electrons and be reduced. Conversely, a more negative value signifies a tendency to lose electrons more readily and act as a reducing agent. This value is determined under standard conditions, which include a concentration of 1 M, a pressure of 1 atm for gases, and a temperature of 25°C (298 K). The standard hydrogen electrode (SHE) is the reference point with a potential of 0.00 V, against which all other electrodes are measured. Understanding the standard reduction potential helps in predicting the direction of electron flow in electrochemical reactions.

Reducing Agents

Reducing agents, or reductants, are substances that donate electrons in a chemical reaction, causing the reduction of another species while getting oxidized themselves. The strength of a reducing agent is indicated by its standard reduction potential. Metals with more negative standard reduction potentials are better reducing agents. They show a greater tendency to donate electrons and undergo oxidation. This property makes them crucial in various industrial processes and in batteries where they facilitate electron flow. For example, consider metals A, B, and C, with standard reduction potentials of +0.5 V, -3.0 V, and -1.2 V, respectively. Metal B, with the most negative potential (-3.0 V), is the strongest reducing agent. It readily donates electrons compared to Metals A and C. Conversely, Metal A, with +0.5 V, is the weakest reducing agent because of its positive tendency to hold electrons rather than losing them.

Electrochemistry

Electrochemistry is the branch of chemistry that deals with the relationship between electrical energy and chemical transformations. It studies how chemical reactions, particularly redox reactions, can generate an electric current, and how electricity can provoke chemical changes. This field is vital for the development of batteries, fuel cells, and electrolysis applications. Electrochemical cells, such as galvanic and electrolytic cells, are central to this study. In a galvanic cell, chemical energy is converted into electrical energy through spontaneous redox reactions. Conversely, an electrolytic cell uses electrical energy to drive non-spontaneous reactions. Understanding electrode potentials within these cells explains how different metals behave as reducing agents or oxidizing agents, linked to their tendency to either donate or accept electrons. The principles of electrochemistry are fundamental in developing energy storage solutions and understanding various biological processes.