7.3 Oxidation−Reduction Reactions Rust forms when the oxygen in the air reacts with iron. In this process, electrons are transferred from one substance to another. Learning Goal Define the terms oxidation and reduction; identify the reactants oxidized and reduced.

Oxidation−Reduction Reactions An oxidation–reduction reaction provides us with energy from food. provides electrical energy in batteries. occurs when iron rusts: 4Fe(s) + 3O2(g)  2Fe2O3(s)

Oxidation−Reduction In an oxidation–reduction reaction, electrons are transferred from one substance to another. OIL RIG Oxidation Is Loss of electrons. Reduction Is Gain of electrons.

Oxidation−Reduction The green patina on the Statue of Liberty is due to the oxidation of copper metal as it forms a green solid, CuO. 2Cu(s)  2Cu2+(s) + 4e− oxidation O2(g) + 4e−  2O2− (s) reduction 2Cu(s) + O2(g)  2CuO(s) Core Chemistry Skill Identifying Oxidized and Reduced Substances

Zn Transfers Electrons to Cu2+ In a single replacement reaction, Zn(s) is oxidized to Zn2+(aq) when it provides two electrons to reduce Cu2+(aq) to Cu(s).

Study Check Identify each of the following as oxidation or reduction: A. Sn(s)  Sn4+(aq) + 4e− B. Fe3+(aq) + 1e−  Fe2+(aq) C. Cl2(g) + 2e−  2Cl− (aq)

Solution Identify each of the following as oxidation or reduction: A. Sn(s)  Sn4+(aq) + 4e− Oxidation B. Fe3+(aq) + 1e−  Fe2+(aq) Reduction C. Cl2(g) + 2e−  2Cl− (aq) Reduction

Study Check In light-sensitive sunglasses, UV light initiates an oxidation–reduction reaction. 2Ag+ + 2Cl−  2Ag + Cl2 A. Which reactant is oxidized? B. Which reactant is reduced? UV light

Solution In light-sensitive sunglasses, UV light initiates an oxidation–reduction reaction. 2Ag+ + 2Cl−  2Ag + Cl2 A. Which reactant is oxidized? chloride ion, Cl− 2Cl−  Cl2 + 2e− B. Which reactant is reduced? silver ion, Ag+ 2Ag+ + 2e−  2Ag UV light

Characteristics of Oxidation and Reduction

Oxidation–Reduction in Biological Systems, Coenzyme FAD The biochemical molecule FAD (flavin adenine dinucleotide) can be reduced to FADH2 by the transfer of two hydrogen atoms (2H+ and 2e−).

Oxidation–Reduction of CH3OH In many biochemical oxidation–reduction reactions, the transfer of hydrogen atoms is necessary for the production of energy. For example, the body metabolizes methyl alcohol, a poisonous substance, by the following reactions: CH3OH  H2CO + 2H Oxidation: loss of H atoms methyl alcohol formaldehyde 2H2CO + O2  2H2CO2 Oxidation: addition of O atoms formaldehyde formic acid 2H2CO2 + O2  2CO2 + 2 H2O Oxidation: addition of O atoms formic acid The intermediate products are toxic, causing headaches and possible death because they interfere with key reactions in cells.

Characteristics, Oxidation−Reduction The particular definition of oxidation and reduction depends on the process that occurs in the reaction. Oxidation always involves a loss of electrons. may also be seen as an addition of oxygen. may also be seen as the loss of hydrogen atoms. Reduction always involves a gain of electrons. may also be seen as the loss of oxygen. may also be seen as the gain of hydrogen.