Classification of reactions in volumetric analysis

1. Acid-base or neutralization reactions, where free bases are reacted with a standard acid (or vice versa). These reactions involve the combination of hydrogen and hydroxide ions to form water.
2. Complex formation reactions, in which the reactants are combined to form a soluble ion or compound. The most important reagent for formation of such complexes is ethylenediamine tetra-acetic acid, EDTA (as the disodium salt).
3. Precipitation reactions, involving the combination of reactants to form a precipitate.
4. Oxidation-reduction reactions, i.e. reactions involving a gain (reduction) or loss (oxidation) of electrons. The standard solutions used here are either oxidizing agents (e.g. potassium permanganate) or reducing agents (e.g. iron (II) compounds).