Question

Which of the following statements is (are) true? Explain. (There may be more than one answer.) a. Oxidation and reduction cannot occur independently of each other. b. Oxidation and reduction accompany all chemical changes. c. Oxidation and reduction describe the loss and gain of electron(s), respectively.

Short answer

Statement a is true. Oxidation and reduction always occur together in a redox reaction as the electrons lost by one species (the reducing agent) are gained by another species (the oxidizing agent). They cannot happen independently. Statement b is false. Not all chemical changes involve oxidation and reduction. Examples of non-redox reactions include acid-base reactions, precipitation reactions, and coordination complex formations. Statement c is true. Oxidation refers to the loss of electron(s) from an atom or molecule, while reduction refers to the gain of electron(s) by an atom or molecule. In a redox reaction, one species undergoes oxidation (loses electrons) and another species undergoes reduction (gains electrons).

Step-by-step solution

Statement a: Oxidation and reduction cannot occur independently of each other.

This statement is true. Oxidation and reduction always occur together in a redox (reduction-oxidation) reaction. Oxidation is the process in which an atom loses one or more electrons, while reduction is the process in which an atom gains one or more electrons. In a redox reaction, the electrons lost by one species (the reducing agent) are gained by another species (the oxidizing agent). Hence, they always occur simultaneously and cannot happen independently.

Statement b: Oxidation and reduction accompany all chemical changes.

This statement is false. Although redox reactions are quite common in chemistry, not all chemical changes involve oxidation and reduction. For example, acid-base reactions, precipitation reactions, and coordination complex formations are examples of non-redox reactions where no electron transfer takes place.

Statement c: Oxidation and reduction describe the loss and gain of electron(s), respectively.

This statement is true. As mentioned before, oxidation refers to the loss of electron(s) from an atom or molecule, while reduction refers to the gain of electron(s) by an atom or molecule. In a redox reaction, one species undergoes oxidation (loses electrons) and acts as the reducing agent, while another species undergoes reduction (gains electrons) and acts as the oxidizing agent.

Key concepts

Oxidation and Reduction

Understanding the dance of electrons during chemical reactions is key to mastering chemistry, and the concepts of oxidation and reduction are central to this understanding. At its simplest, oxidation is the process where an atom or molecule loses electrons. This can often result in an increase in the oxidation state of the substance. On the other hand, reduction takes place when an atom or molecule gains electrons, often leading to a decrease in its oxidation state.

Oxidation and reduction always happen together; they're like the two sides of the same coin and occur simultaneously during a redox reaction. To illustrate this concept, imagine a simple redox reaction, such as the rusting of iron. When iron rusts, it loses electrons (it is oxidized) and oxygen gains those electrons (it is reduced). This interplay is a classic example of a redox process.

To aid in mastering these concepts, remember the mnemonic 'LEO says GER': Lose Electrons Oxidation, Gain Electrons Reduction.

Chemical Changes

Chemical changes are transformations that alter the composition and identity of substances involved. These changes result in the formation of new chemical substances with properties different from those of the original substances. It's important to recognize that not all chemical changes are redox reactions involving electron transfer. For instance, when an acid reacts with a base, they form a salt and water in an acid-base reaction—this process doesn't entail the transfer of electrons but the transfer of a proton, or hydrogen ion.

Similarly, when sugar dissolves in water, it dissipates into individual molecules but retains its chemical identity, which is a physical rather than a chemical change. Understanding the types of chemical reactions, including their signs, like color change, temperature change, gas production, or precipitate formation, can further clarify the concept of chemical changes.

Electron Transfer

Electron transfer is the movement of electrons from one entity to another and is the defining feature of redox reactions. Electrons are transferred during these reactions because atoms aim to gain a stable electronic configuration, often achieved through a full outer electron shell. This transfer can be direct, as in the case of metal corrosion, or indirect, such as in the operation of a battery where electrons move through an external circuit.

In redox chemistry, identifying the number of electrons exchanged can be crucial to balancing redox equations. In more advanced concepts, understanding electron transfer is key for topics like electrochemistry, where electron flow generates electric current, or in biological systems, where the transfer of electrons in metabolic pathways is fundamental for the production of energy.