Problem 53 - A Complete Resource Book in Chemistry for JEE Main

Question

The standard reduction potential values of three metallic cations X, Y, and \(Z\) are \(0.52,-3.03\) and \(-1.18\) respectively. The order of reducing power of the corresponding metal is (a) \(\mathrm{Y}>\mathrm{Z}>\mathrm{X}\) (b) \(\mathrm{X}>\mathrm{Y}>\mathrm{Z}\) (c) \(\mathrm{Z}>\mathrm{Y}>\mathrm{X}\) (d) \(\mathrm{Z}>\mathrm{X}>\mathrm{Y}\)

Step-by-Step Solution

Answer

The order of reducing power is \(Y > Z > X\), matching option (a).

Step 1: Understanding Reduction Potential

Reduction potential (\(E^0\)) indicates the tendency of a species to gain electrons and be reduced. A more positive \(E^0\) value means a stronger tendency to gain electrons and become reduced.

Step 2: Identifying Reducing Agents

The stronger the reducing agent, the more it can give away electrons, which correlates with a less positive (or more negative) reduction potential. Hence, a metal with a lower \(E^0\) value is a stronger reducing agent.

Step 3: Compare Reduction Potentials

The given standard reduction potentials are: \(X: 0.52\), \(Y: -3.03\), and \(Z: -1.18\). Compare these values to determine which metal is the strongest reducing agent. \(Y\) has the lowest reduction potential, making it the strongest reducing agent, then \(Z\), followed by \(X\).

Step 4: Determine Order of Reducing Power

Based on the comparison, the order of reducing power from strongest to weakest is: \(Y > Z > X\).

Step 5: Choose the Correct Option

From the options given, the order \(Y > Z > X\) corresponds to option (a).

Key Concepts

Reduction Potential

Every chemical species has a natural inclination to either gain or lose electrons. The reduction potential is a quantitative measure of this tendency. Specifically, it is the potential difference (voltage) at which a species will gain electrons and become reduced. In electrochemistry, it is commonly denoted as \( E^0 \).
Reduction potential is highly significant because it allows us to predict the likelihood of a chemical reaction occurring. A positive \( E^0 \) implies that the species is more forward-oriented in accepting electrons, in other words, a stronger oxidizing agent. Conversely, a negative \( E^0 \) suggests a reluctance to accept electrons, indicating a lesser tendency for reduction.
For instance, in the context of the exercise, the metals \( X \), \( Y \), and \( Z \) all have different reduced states due to their given potentials, 0.52, -3.03, and -1.18, respectively. \( X \) has a positive \( E^0 \), suggesting it is more inclined to undergo reduction compared to \( Y \) and \( Z \). This means that \( X \) is a weaker reducing agent when compared to \( Y \) and \( Z \).

Reducing Agent

Reducing agents play a crucial role in chemical reactions, particularly in oxidation-reduction (redox) processes. A strong reducing agent donates electrons easily and helps another compound reduce, or gain electrons. This means that it itself gets oxidized in the process. The strength of a reducing agent is inversely related to its reduction potential—a lower (or more negative) reduction potential indicates a stronger reducing agent.
When evaluating the reducing power of different substances, remember that:

• Substances with lower \( E^0 \) are better reducers.
• They are more likely to donate electrons and get oxidized.

In the problem provided, metal \( Y \) is the most potent reducing agent because it has the most negative reduction potential (-3.03). This means \( Y \) most readily loses electrons, overpowering \( Z \) and \( X \) in reducing strength. This gives the order \( Y > Z > X \) in terms of reducing power.

Electrochemical Series

The electrochemical series, also known as the activity series, is a list of elements organized by their standard reduction potential values. It provides valuable insights into the reactivity of metals and other species within redox reactions. By reviewing this series, you can quickly determine which metals are more likely to oxidize or reduce in chemical interactions.
Here are a few points to note about the electrochemical series:

• Species at the top, with higher \( E^0 \), are superior oxidizing agents and poorer reducing agents.
• Species lower in the series are stronger reducing agents and are prone to oxidizing.

Considering the exercise, by arranging \( X \), \( Y \), and \( Z \) on the electrochemical series based on their \( E^0 \) values, you reveal \( Y \) as the lowest, making it the supreme reducer. This proves it's significance in predicting interactions between different chemical species.