Question

Which statement is incorrect? (1) Oxidation of a substance is followed by reduction of another. (2) Reduction of a substance is followed by oxidation of another. (3) Oxidation and reduction are complimentary reactions. (4) It is not necessary that both oxidation and reduction should takes place in the same reaction.

Short answer

Statement 4 is incorrect.

Step-by-step solution

- Understand Oxidation and Reduction

Oxidation is the process in which a substance loses electrons, while reduction is the process in which a substance gains electrons. These two processes always occur together in a redox (reduction-oxidation) reaction.

- Analyze Statement 1

Statement 1: 'Oxidation of a substance is followed by reduction of another.' This is correct because in a redox reaction, when one substance loses electrons (oxidation), another substance gains those electrons (reduction).

- Analyze Statement 2

Statement 2: 'Reduction of a substance is followed by oxidation of another.' This is also correct because the process of one substance gaining electrons (reduction) is naturally accompanied by another substance losing electrons (oxidation).

- Analyze Statement 3

Statement 3: 'Oxidation and reduction are complimentary reactions.' This is correct because both processes must occur together as part of a redox reaction.

- Analyze Statement 4

Statement 4: 'It is not necessary that both oxidation and reduction should take place in the same reaction.' This statement is incorrect. In every redox reaction, oxidation and reduction always happen simultaneously. If one substance is oxidized, another must be reduced.

Key concepts

Oxidation

Oxidation is an essential concept in chemistry that involves the loss of electrons from a substance. When a substance undergoes oxidation, it loses electrons and generally increases its oxidation state. This process is fundamental to various chemical reactions, particularly in the formation of compounds.

For instance, when iron rusts, it undergoes oxidation. The iron combines with oxygen in the air, and electrons are transferred from the iron to the oxygen. This process transforms the iron into iron(III) oxide, commonly known as rust.

The key takeaway is that any time a substance loses electrons, it is considered oxidized. Understanding this principle helps in recognizing many chemical phenomena around us.

Reduction

Reduction is the counterpart to oxidation and involves the gain of electrons by a substance. When a substance gains electrons, it undergoes reduction and decreases its oxidation state. This process is equally crucial in chemical reactions.

Consider the example of hydrogen gas reacting with oxygen to form water. In this reaction, oxygen gains electrons from hydrogen. Here, oxygen is reduced to form water. This gain of electrons is characteristic of all reduction processes.

It's important to remember that reduction cannot occur alone; it must be paired with oxidation. This is why these reactions are called redox reactions – a combination of reduction and oxidation.

Electron Transfer

Electron transfer is at the heart of redox reactions. It involves the movement of electrons from one substance to another. This transfer is what links oxidation and reduction, making them complementary reactions that occur simultaneously in every redox process.

For example, in the reaction between zinc and copper(II) sulfate, electrons are transferred from zinc to copper ions. Zinc loses electrons (oxidized) while copper ions gain electrons (reduced).

Understanding electron transfer mechanisms is crucial for explaining how energy is produced and consumed in chemical reactions, including those that occur in batteries, respiration, and photosynthesis. These processes all rely on the movement of electrons to store and release energy efficiently.