Problem 60 - A Complete Resource Book in Chemistry for JEE Main

Question

Transition metals despite having higher values of standard reduction potentials, are poor reducing agents. This is due to (a) low heat of hydration (b) high ionization energies (c) low ionization energies (d) high enthalpy of vapourization

Step-by-Step Solution

Answer

Transition metals are poor reducing agents due to high ionization energies (Option b).

Step 1: Understanding Reducing Agents

A reducing agent is a substance that loses electrons and gets oxidized in a chemical reaction. The effectiveness of a reducing agent is often related to its ability to donate electrons readily.

Step 2: Evaluating Standard Reduction Potentials

Transition metals have high standard reduction potentials, meaning they have a greater tendency to gain electrons rather than lose them. This indicates they are not naturally inclined to be reducing agents, which correlates with higher electron affinities.

Step 3: Analyzing Ionization Energies

Transition metals exhibit high ionization energies due to their stable electron configurations. The high ionization energy means that more energy is required to remove electrons, making them less efficient as reducing agents.

Step 4: Exploring Other Factors

While factors like heat of hydration, ionization energies, and enthalpy of vaporization can affect the chemistry of metals, in the context of being reducing agents, high ionization energies are the most relevant factor among the given options.

Key Concepts

Standard Reduction Potential

The standard reduction potential is a measure of a substance's tendency to gain electrons. It is represented in volts and is determined under standard conditions, typically at 1 M concentration, 1 atm pressure, and 25°C temperature. When substances have high standard reduction potentials, they are more likely to undergo reduction, meaning they have a strong affinity for electrons. Transition metals often have high standard reduction potentials compared to other elements. This implies that they prefer gaining electrons to achieve a stable electron configuration. This property makes them less likely to act as reducing agents, since reducing agents are substances that donate electrons to other elements. In simple terms:

• High standard reduction potential = strong tendency to gain electrons.
• Low standard reduction potential = strong tendency to lose electrons and get oxidized.

Ionization Energy

Ionization energy is the energy needed to remove an electron from an atom in its gaseous state. It reflects how strongly an atom's nucleus holds onto its electrons. For transition metals, this energy is quite high, which means that removing an electron is not an easy task. Transition metals have unique electron configurations that contribute to their stability. They tend to fill the d-sublevel, which provides additional stability and results in higher ionization energy. The high ionization energies explain why transition metals are not efficient reducing agents. They prefer to retain their electrons, making them less inclined to donate electrons during chemical reactions. Here's a quick breakdown:

• High ionization energy = more energy needed to remove electrons.
• High ionization energy = poor reducing agent capacity.

Reducing Agents

Reducing agents play a critical role in chemical reactions, particularly in redox reactions. A reducing agent is oxidized in the process, meaning it loses electrons while causing another substance to be reduced by gaining electrons. The strength of a reducing agent is determined by its ability to give up electrons easily. If a substance has a high tendency to lose electrons, it's considered a good reducing agent. In contrast, transition metals are poor reducing agents because:

• They have high ionization energies, requiring lots of energy to lose electrons.
• They possess high standard reduction potentials, meaning they tend to gain rather than lose electrons.

These characteristics illustrate why transition metals are more likely to act as oxidizing agents instead, fostering conditions for electron gain rather than loss.