Question

In self-reduction, the reducing species is A) \(\mathrm{S}\) B) \(\mathrm{O}^{2-}\) C) \(\mathrm{S}^{2-}\) D) \(\mathrm{SO}_{2}\)

Short answer

\(\mathrm{SO}_{2}\) is the reducing species in self-reduction.

Step-by-step solution

Understanding Self-Reduction

Self-reduction is a process in which a substance acts both as a reducing agent and as an oxidizing agent. This means the same substance gets oxidized as well as reduced during the reaction.

Identifying the Species that Undergoes Self-Reduction

To undergo self-reduction, a species must exist in multiple oxidation states such that it can both accept and donate electrons to itself. Among the given options, only \(\mathrm{SO}_{2}\) has the capability to both get reduced to sulfur (\(\mathrm{S}\)) and oxidized to sulfate (\(\mathrm{SO}_{4}^{2-}\)), acting as a reducing and oxidizing agent.

Key concepts

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are fundamental chemical processes where the oxidation state of atoms are changed through the transfer of electrons. In these reactions, one species loses electrons and is oxidized, while another gains electrons and is reduced. It's important to understand that reduction and oxidation always occur together—it’s a reciprocal process.

Examples in Everyday Life

Simple examples of redox reactions include the rusting of iron or the browning of fruit. In both cases, the substances involved are undergoing electron transfer leading to a change in their oxidation states.

Oxidation States

Understanding oxidation states is crucial for mastering redox reactions. An oxidation state is a numerical indicator of the degree of oxidation of an atom in a compound. It’s a hypothetical charge that an atom would have if all bonds were purely ionic. This concept is applied as a bookkeeping tool to keep track of electrons in chemical reactions.

Determining Oxidation States

Oxidation states can generally be determined by following a set of rules such as: oxygen usually has an oxidation state of -2 (exception being peroxides); hydrogen is +1 when bonded to non-metals and -1 when bonded to metals; and the sum of the oxidation states for all atoms in a neutral molecule must equal zero.

Chemical Reducing Agents

Chemical reducing agents are substances that bring about reduction by donating electrons to other substances and, in the process, they get oxidized. These agents are vital in redox reactions as they are the source of electrons that another species requires to be reduced.

Characteristics and Examples

Reducing agents have certain characteristics; they are often metals or hydrides, possess a low electronegativity, and have a tendency to form positive ions. Examples of common reducing agents include hydrogen gas, metals like zinc or iron, and compounds like sodium bisulfite. In electrochemistry, reducing agents supply the electrons for the reduction half of a redox reaction in an electrochemical cell.