Question

Reduction can be defined as a gain of electrons or as a decrease in oxidation state. Explain why the two definitions mean the same thing, and give an example to support your explanation.

Short answer

Reduction can be defined as a gain of electrons or a decrease in oxidation state. Both definitions essentially describe the same underlying process: a change in electron configuration within a chemical species. When a species gains electrons, its total positive charge decreases, or its negative charge increases, leading to a decrease in its oxidation state. Conversely, a decrease in the oxidation state means the species has gained electrons. An example supporting this explanation is the reduction of a copper (II) ion (Cu²⁺) to metallic copper (Cu). In this reaction, the copper (II) ion gains 2 electrons, and its oxidation state decreases from +2 to 0, illustrating that both gain of electrons and decrease in oxidation state correspond to the phenomenon of reduction.

Step-by-step solution

Definition 1: Gain of Electrons

Reduction can be defined as a gain of electrons by an atom, ion, or molecule. When a chemical species undergoes reduction, the number of electrons that it carries increases, resulting in a reduced form of the original species. The addition of electrons can lead to several changes like decreasing the total positive charge or increasing the negative charge of the chemical species. This results in change in the oxidation state of the species

Definition 2: Decrease in Oxidation State

Oxidation state is a number that describes the degree of oxidation of an element within a chemical compound. Essentially, it represents how many electrons have been lost or gained by a particular element, and it can be positive, negative, or zero depending on the chemical species. When the oxidation state of a species decreases, it means that it has undergone reduction. In other words, the species has gained electrons and its oxidation state has decreased in the process.

Relationship between the two definitions

Both definitions of reduction focus on the change in electron configuration within a chemical species. Gain of electrons leads to a decrease in the oxidation state, and conversely, a decrease in the oxidation state implies that the species has gained electrons. As both definitions reflect the same underlying process - change in electron configuration - they effectively describe the same phenomenon of reduction.

Example: Reduction of Copper (II) Ion

Let's consider the reduction of a copper (II) ion (Cu²⁺) to metallic copper (Cu): Cu²⁺(aq) + 2e⁻ → Cu(s) In this reaction, the copper (II) ion gains 2 electrons and is reduced to form copper atoms. The oxidation state of copper decreases from +2 (in Cu²⁺) to 0 (in Cu). This example demonstrates both the gain of electrons and the decrease in oxidation state associated with reduction and affirms that both definitions mean the same thing.

Key concepts

Oxidation State

The term "oxidation state" is crucial in understanding chemical reactions, especially in terms of redox reactions. It serves as a convenient way to keep track of electrons in atoms, ions, and molecules.

The oxidation state is a numerical value that describes how many electrons an atom has gained or lost compared to its neutral state. When an atom loses electrons, it attains a positive oxidation state, implying it has undergone oxidation. Conversely, when it gains electrons, it attains a negative oxidation state, indicating reduction.

For instance, in the case of a copper ion (Cu²⁺), it has lost 2 electrons and thus, it possesses an oxidation state of +2. During reduction, if this ion gains 2 electrons, its oxidation state decreases to 0 as it returns to its elemental form, demonstrating the basic idea of electron gain and consequent reduction in oxidation state.

Electron Gain

Electron gain refers to the fundamental process during reduction where an atom, ion, or molecule acquires additional electrons. This acquisition increases the negative charge of the chemical species or neutralizes a positive charge.

In a chemical reaction, gaining electrons results in reduced chemical species. For example, the copper ion (Cu²⁺) in an aqueous solution can gain 2 electrons to become copper metal (Cu), which has no charge. Each gained electron lowers the oxidation state, indicating a direct relationship between electron gain and a decrease in oxidation state.

The concept is straightforward: any process that adds electrons to a species is classified as reduction. This is an essential part of redox reactions, where balanced electron exchanges maintain the electron count across the reaction's entirety.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are chemical processes that involve the transfer of electrons between two species. During these reactions, one species undergoes oxidation, losing electrons, while the other undergoes reduction, gaining electrons.

This interplay between electron loss and gain is pivotal in diverse processes, from cellular respiration in biology to industrial chemical processes. Redox reactions are often defined by half-reactions, one for oxidation and one for reduction. For example, in the reaction involving the copper ion (Cu²⁺) becoming copper metal (Cu), copper gains electrons, and therefore, undergoes reduction.

The balancing act between oxidation and reduction highlights the conservation of charge in chemical reactions, as the total number of electrons stays constant, shifting from one species to another. Understanding redox reactions is fundamental to grasping how chemical changes occur and why they are essential in both natural and synthetic settings.