Oxidation-Reduction Reactions Introduction

The term oxidation originally referred to the combination of a substance with oxygen. This results in an increase in the oxidation state of an element in that substance. According to the original definition, the following reactions involve oxidation of the substance shown on the far left of each equation. Oxidation states are shown for one atom of the indicated kind. 

Originally, reduaion described the removal of oxygen from a compound. Oxide ores are reduced to metals (a very real reduction in mass). For example, tungsten for use in light bulb filaments can be prepared by reduction of tungsten(VI) oxide with hydrogen at 1200°C  

Tungsten is reduced, and its oxidation state decreases from +6 to zero. Hydrogen is oxidized from zero to the +1 oxidation state. The terms oxidation and reduction are now applied much more broadly. 

Oxidation is an increase in oxidation state and corresponds to the loss, or apparent loss, of electrons. Reduction is a decrease in oxidation state and corresponds to a gain, or apparent gain, of electrons. 

Electrons are neither created nor destroyed in chemical reactions. So oxidation and reduction always occur simultaneously, and to the same extent, in ordinary chemical reactions. In the four equations cited previously as examples of oxidation, the oxidation states of iron and carbon atoms increase as they are oxidized. In each case oxygen is reduced as its oxidation state decreases from zero to -2. 

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OXIDATION STATES AND OXIDATION REDUCTION REACTIONS (INTRODUCTION AND SECTION 20.1) In this chapter, we have focused on electrochemistry, the branch of chemistry that relates electricity and chemical reactions. Electrochemistry involves oxidation-reduction reactions, also called redox reactions. These reactions involve a change in the oxidation state of one or more elements. In every oxidation-reduction reaction one substance is oxidized (its oxidation state, or number, increases) and one substance is reduced (its oxidation state, or number, decreases). The substance that is oxidized is referred to as a reducing agent, or reductant, because it causes the reduction of some other substance. Similarly, the substance that is reduced is referred to as an oxidizing agent, or oxidant, because it causes the oxidation of some other substance. 

Ferroin With the introduction of Ce(IV) as an oxidant and the evaluation of the formal potential of the Ce(rV)-Ce(III) couple, the need for indicators with higher electrode potentials became evident. The indicator ferroin, tris(l,10-phenanthroline)-iron(II), was discovered by Walden, Hammett, and Chapman, and its standard potential was evaluated at 1.14 V. Hume and KolthofiF found that the formal potential was 1.06 V in 1 M hydrochloric or sulfuric acid. The color change, however, occurs at about 1.12 V, because the color of the reduced form (orange-red) is so much more intense than that of the oxidized form (pale blue). From Figure 15-1 it can be seen that ferroin should be ideally suited to titrations of Fe(II) and other reductants with Ce(lV), particularly when sulfuric acid is the titration medium. It has the further advantages of undergoing a reversible oxidation-reduction reaction and of being relatively stable even in the presence of oxidant. 

Gray, Harry B., John D. Simon, and William C. Trogler. Braving the Elements. Sausalito, Calif. University Science Books, 1995. This book is an introduction to the basic principles of chemistry, with elementary explanations of radioactive decay, chemical bonding, oxidation-reduction reactions, and acid-base chemistry. Practical applications of specific chemical compounds and classes of compounds are presented. 

Balancing Oxidation-Reduction Reactions by the Half-Reaction Method 1 7.5 Electrochemistry An Introduction 1 7.6 Batteries 1 7.7 Corrosion 1 7.8 Electrolysis... 

The inorganic elements in aqueous solution reactions, both acid-base complex formation, precipitation and oxidation/reduction, frequently come rapidly to equilibrium when no more reactions are possible. The implication is that in the environment and in organisms many of their properties cannot change unless circumstances change, for example the introduction of new components. 

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