Introduction

Definition. Electrochemistry is the study of the interconversion of chemical and electric energy.

Scope. This section discusses the fundamental principles of electrochemistry and the application of these principles to commercial operations. Detailed discussions are given of the conversion of electrical to chemical energy (electrodeposition, electrolytic refining, electrowinning, and electrosynthesis); only brief discussions, with particular reference to basic principles, are given for the devices converting chemical to electrical energy (batteries and fuel cells) because these are discussed in Secs. 11.10 and 11.11.

Electrolytes. Electrolytic solutions contain charged particles called ions which are atoms or groups of atoms which have lost or gained electrons and, as a result, are positively or negatively charged, respectively. Negatively charged ions are called anions, and positively charged ions are called cations. The electrolyte may comprise a solvent water, an organic liquid, a fused (or molten) salt, or a solid. Since the electrolyte is electrically neutral, the number of anions and cations must be equal.

In aqueous solutions (the most common solvent used in practice), electrolytic solutions are formed by dissolving a salt, an acid, or a base in water. These compounds may then be completely or partially dissociated into ions. Salts, such as copper sulfate (CuSO ₄), silver nitrate (AgNO ₃), and sodium chloride (NaCl); acids, such as sulfuric acid (H ₂SO ₄), hydrochloric acid (HCl), and nitric acid (HNO ₃