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

The two definitions of reduction - gain of electrons and decrease in oxidation state - mean the same thing because when an element gains electrons, its oxidation state decreases due to the increase in negative charge from the added electrons. A decrease in the oxidation state signifies reduction. For example, in the reaction between copper(II) ions (Cu^2+) and zinc metal (Zn), copper gains two electrons from zinc, leading to a decrease in its oxidation state from +2 to 0. This demonstrates that a gain of electrons results in a decrease in oxidation state, supporting the equivalence of the two definitions.

Step-by-step solution

Definition of Oxidation State

An oxidation state is a number assigned to an element in a chemical compound that represents the number of electrons it has either gained or lost compared to its neutral atom. In general, the oxidation state of an element increases when it loses electrons and decreases when it gains electrons.

Reduction as Gain of Electrons

Reduction is a chemical reaction in which an element gains electrons. As a result, the element is said to be reduced. When an element gains electrons, it acquires more negative charge, which leads to a decrease in its oxidation state.

Relation between Gain of Electrons and Decrease in Oxidation State

When an element gains electrons, its oxidation state decreases because it has more negative charges due to the added electrons. Thus, gaining electrons and decreasing oxidation state mean the same thing for a reduction process.

Example of Reduction

Let's use the reaction between copper(II) ions and zinc metal as an example: Cu^2+ (aq) + Zn (s) -> Cu (s) + Zn^2+ (aq) In this reaction, the copper(II) ions (Cu^2+) gain two electrons from the zinc metal (Zn) to form metallic copper (Cu). This process is reduction because electrons are gained. The oxidation state of copper decreases from +2 in Cu^2+ to 0 in Cu, demonstrating that a gain of electrons results in a decrease in oxidation state.