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

Question

The standard reduction potential values of three metallic cations \(\mathrm{X}, \mathrm{Y}\), and \(\mathrm{Z}\) 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

(a) Y > Z > X

Step 1: Identify Standard Reduction Potentials

Firstly, identify the given standard reduction potentials for metals X, Y, and Z: X = 0.52 V, Y = -3.03 V, and Z = -1.18 V. These values indicate how readily the metal cations accept electrons to be reduced.

Step 2: Understand the Concept of Reducing Power

The reducing power of a metal is inversely related to its reduction potential. A lower (or more negative) reduction potential indicates a stronger reducing agent, as it is more likely to lose electrons and undergo oxidation.

Step 3: Arrange the Reduction Potentials

Arrange the metals according to their reduction potentials from lowest to highest: Y (-3.03 V), Z (-1.18 V), X (0.52 V). This arrangement shows the tendency of each metal to accept electrons.

Step 4: Translate Reduction Potentials to Reducing Power

Since reducing power is inversely related to the reduction potential, the order from strongest to weakest reducing power is the reverse of the order of reduction potentials: Y > Z > X.

Step 5: Select the Correct Option

From the options provided, compare the order derived from the analysis Y > Z > X to get the correct order of reducing power. The correct choice is (a) Y > Z > X.

Key Concepts

Reduction Potentials

In electrochemistry, reduction potential plays a pivotal role in understanding how substances behave during chemical reactions. It tells us about the tendency of a species to gain electrons and be reduced. This value is measured in volts (V), and standard reduction potentials are typically provided in tables at standard conditions (298 K, 1 atm, and 1M concentration). The more positive the reduction potential, the greater the tendency to accept electrons.

In the exercise given, the reduction potential values for metals X, Y, and Z were provided as 0.52 V, -3.03 V, and -1.18 V respectively. These values indicate how likely each metal cation is to be reduced:

• A positive value (e.g., X = 0.52 V) suggests a stronger ability to gain electrons and be reduced.
• A negative value means the species is less eager to accept electrons.

However, it's essential to remember that a more negative reduction potential is indicative of a stronger reducing agent.

Reducing Power

The term 'reducing power' refers to the potential of a substance to donate electrons. When discussing reducing power, it's all about how easily a substance can lose electrons and cause another substance to be reduced. This is the opposite of what reduction potential indicates.

Reducing power is inversely related to reduction potential. Therefore, if a metal has a lower (or more negative) reduction potential, it means it has a higher reducing power, as it will more readily donate its electrons:

• A strong reducing agent has a more negative reduction potential.
• Metals like Y, with a reduction potential of -3.03 V, have a high reducing power.

Thus, in our exercise, metal Y, with the most negative reduction potential, was identified as having the strongest reducing power, whereby it easily loses electrons compared to metals Z and X.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, or redox reactions, form the basis of various processes in chemistry, from biological systems to industrial processes. A redox reaction involves the transfer of electrons between two substances.

In these reactions:

• Oxidation is the loss of electrons. This is what reducing agents do.
• Reduction is the gain of electrons. This happens to the oxidizing agent.

Understanding this electron transfer is crucial because it determines the roles substances play in the reaction.

Considering the exercise, metals Y and Z, with negative standard reduction potentials, act as strong reducing agents (they lose electrons). Metal X, with a positive reduction potential, is a better oxidizing agent (it gains electrons). Knowing which substance has the greater reducing power helps predict the direction and feasibility of redox reactions effectively.