Question

Tell for each of the following substances whether the oxidation number increases or decreases in a redox reaction: (a) An oxidizing agent (b) A reducing agent (c) A substance undergoing oxidation (d) A substance undergoing reduction

Short answer

(a) Decreases, (b) Increases, (c) Increases, (d) Decreases.

Step-by-step solution

Understanding Oxidizing Agent

An oxidizing agent is a substance that oxidizes another substance by accepting electrons. In the process, the oxidizing agent itself gets reduced. Therefore, the oxidation number of an oxidizing agent decreases as it gains electrons.

Understanding Reducing Agent

A reducing agent is a substance that reduces another by donating electrons. As it donates electrons, the reducing agent itself gets oxidized. Therefore, the oxidation number of a reducing agent increases as it loses electrons.

Substance Undergoing Oxidation

A substance undergoing oxidation loses electrons during a chemical reaction. As it loses electrons, its oxidation number increases.

Substance Undergoing Reduction

A substance undergoing reduction gains electrons in a chemical reaction. As it gains electrons, its oxidation number decreases.

Key concepts

Oxidizing Agent

An oxidizing agent is crucial in redox reactions because it plays the role of accepting electrons from another substance. By accepting these electrons, the oxidizing agent causes the other substance to become oxidized.
This means that the substance itself undergoes reduction. Reduction involves the gain of electrons, which results in a decrease in the oxidation number of the oxidizing agent.
For example, in a reaction where iron rusts, oxygen acts as the oxidizing agent by accepting electrons from iron. As a result, oxygen's oxidation number decreases as it is reduced.
Remember:

• Oxidizing agents gain electrons
• Oxidizing agents undergo reduction
• Oxidation number of oxidizing agents decreases

Reducing Agent

A reducing agent is equally important in redox reactions but functions oppositely to an oxidizing agent. Reducing agents donate electrons to another substance, thus facilitating the reduction of that substance.
As the reducing agent loses electrons during this process, it undergoes oxidation, which is characterized by an increase in its oxidation number.
For instance, hydrogen gas acts as a reducing agent when it reacts with oxygen to form water. In this reaction, hydrogen donates electrons to oxygen, resulting in hydrogen's oxidation number increasing.
It's important to remember:

• Reducing agents lose electrons
• Reducing agents undergo oxidation
• Oxidation number of reducing agents increases

Redox Reactions

Redox reactions are a fascinating type of chemical reaction where the transfer of electrons occurs between substances. These reactions are key to many processes, such as cellular respiration and combustion.
Redox is short for reduction-oxidation, signifying that these reactions involve both reduction (gain of electrons) and oxidation (loss of electrons).
A classic example of a redox reaction is when iron rusts upon exposure to oxygen and moisture; here, iron oxidizes as it loses electrons, while oxygen reduces by gaining those electrons.
Key points about redox reactions:

• Involves transfer of electrons
• Comprises both oxidation and reduction
• Is foundational in a variety of chemical and biological processes

Electron Transfer

Electron transfer is the cornerstone of redox reactions. This movement of electrons from one substance to another is what defines a redox process.
Electrons are negatively charged particles, and their movement leads to changes in oxidation numbers of substances.
During a redox reaction, one substance loses electrons and is oxidized, while another substance gains these electrons and is reduced. Understanding this transfer helps in recognizing how substances change during chemical reactions.
Remember these aspects about electron transfer:

• Electrons move between substances
• Causes changes in oxidation numbers
• Is essential for both oxidation and reduction processes