Question

True or false: (a) Reduction occurs if the oxidation number of an element increases. (b) Oxidation and reduction must occur together in a reaction.

Short answer

(a) False, (b) True.

Step-by-step solution

Understanding Reduction

Reduction refers to the gain of electrons by a molecule, atom, or ion. A key indicator of reduction is the decrease in the oxidation number of an element.

Understanding Oxidation

Oxidation involves the loss of electrons from a molecule, atom, or ion. This is characterized by the increase in the oxidation number of an element, which is the opposite of reduction.

Analyzing Statement (a)

The statement claims that reduction occurs when the oxidation number of an element increases. This is incorrect; an increase in the oxidation number indicates oxidation, not reduction. Therefore, statement (a) is false.

Understanding Redox Reactions

In any chemical reaction, if one species gains electrons (is reduced), another must lose electrons (is oxidized). This is called a redox (reduction-oxidation) reaction and is how electrons are conserved.

Analyzing Statement (b)

Since oxidation involves loss and reduction involves gain of electrons, they must occur simultaneously in a reaction. Thus, statement (b) is true.

Conclusion

Conclude based on previous analyses: (a) False, as reduction corresponds to a decrease in oxidation number, and (b) True, since oxidation and reduction occur together in redox reactions.

Key concepts

Oxidation

In chemistry, oxidation is a fundamental concept often involved in reactions known as redox (reduction-oxidation) reactions.
Oxidation is characterized by the loss of electrons from a molecule, atom, or ion.
As a result of losing electrons, the oxidation number of an element increases. You can think of oxidation as the process of an element becoming more 'positive' since electrons, which are negatively charged, are being lost.
Understanding oxidation is crucial because it is one half of a redox reaction. Here are some key points to remember about oxidation:

• It involves the increase in the oxidation number of an element.
• Electrons are lost during this process.
• Oxidation cannot happen independently; it must occur alongside reduction in a redox reaction.

Let's use an example to simplify: in the reaction where iron forms rust, iron ( ext{Fe}) loses electrons and becomes oxidized, forming iron oxide, commonly known as rust.

Reduction

Reduction is a fascinating and crucial part of redox reactions, complementing the process of oxidation.
When a substance undergoes reduction, it gains electrons. This gain of electrons decreases the oxidation number of an element involved in the process, making it more 'negative.'
The connection between the gain of electrons and reduction is sometimes remembered by the mnemonic 'OIL RIG' - Oxidation Is Loss, Reduction Is Gain. Here are some essential aspects of reduction:

• It involves the decrease in the oxidation number of an element.
• Electrons are gained during this process.
• Reduction occurs simultaneously with oxidation in a redox reaction.

A daily life example of reduction is the gain of electrons by oxygen when it reacts with hydrogen to form water ( ext{H}_2 ext{O}), where oxygen is reduced.

Oxidation Numbers

Oxidation numbers are a way to keep track of how many electrons an atom has gained or lost in a reaction.
It provides a very useful tool for identifying which elements are oxidized or reduced in a chemical reaction.
Oxidation numbers serve as a bookkeeping method in chemistry, representing the charge an atom would have if the compound was composed of ions. Here are key points about oxidation numbers:

• They help determine which elements have undergone oxidation or reduction.
• An increase in oxidation number indicates oxidation, while a decrease indicates reduction.
• Oxidation numbers can be positive, negative, or zero, depending on the element and its state.

Understanding oxidation numbers can help you balance chemical equations and identify changes in election configurations in reactions, making them indispensable in studying redox reactions.