Question

(a) What is meant by the term reduction? (b) On which side of a reduction half-reaction do the electrons appear? (c) What is meant by the term reductant? (d) What is meant by the term reducing agent?

Short answer

a) Reduction is the process of a species gaining one or more electrons in a chemical reaction. It always occurs alongside oxidation, forming redox reactions. b) In a reduction half-reaction, electrons appear on the reactant side (left side), as seen in this example: \(Cu^{2+} (aq) + 2 e^{-} \rightarrow Cu (s)\) c) A reductant, or reducing agent, donates electrons to another species in a redox reaction, causing the reduction of that species while becoming oxidized itself. d) Reducing agents, or reductants, are substances that donate electrons to other species during redox reactions, causing the reduction of that species while undergoing oxidation themselves. Hydrogen gas is a common example of a reducing agent.

Step-by-step solution

a) Reduction

: Reduction is a chemical reaction in which a species gains one or more electrons. It is the opposite of oxidation, where a species loses electrons. Reduction and oxidation reactions always occur together, which is why they are commonly referred to as redox reactions.

b) Side of electrons appearing in a reduction half-reaction

: In a reduction half-reaction, electrons appear on the reactant side (left side) of the equation. This is because the species is gaining electrons in the process of reduction. For example, in the reduction half-reaction: \(Cu^{2+} (aq) + 2 e^{-} \rightarrow Cu (s)\) Electrons (2 e^{-}) appear on the left side as reactants, showing that they are gained by the copper (II) ion in the process of being reduced to copper metal.

c) Reductant

: A reductant, also known as a reducing agent, is a chemical species that donates electrons to another species in a redox reaction, causing the reduction of that species. By donating electrons, the reductant itself gets oxidized in the process.

d) Reducing agent

: A reducing agent, also known as a reductant, is a substance that donates electrons to another species during a redox reaction, thereby causing the reduction of that species. In the process of donating electrons, the reducing agent itself undergoes oxidation. A common example of a reducing agent is hydrogen gas, which donates electrons to other species, becoming oxidized to form hydrogen ions (H+).