pH and ORP

摘要

The term "pH" is used to express the degree of acidity or alkalinity of a solution. Although many different ions may be formed in solution, those that establish whether the solution is acid or alkaline are the hydrogen (H~+) and the hydroxyl (OH~-) ions, respectively. When the hydrogen ions exceed the hydroxyl ions in number, the solution is acid. When they are equal, the solution is neutral. Alkalinity (or basicity) denotes that the hydroxyl ions exceed the hydrogen ions. Acids and alkalis vary in the degree to which they form ions in solution. Those that almost completely ionize are called strong acids or bases. Hydrochloric acid and sodium hydroxide are examples. Other acids and bases ionize to only a small degree and are called weak acids or bases. Acetic acid and ammonium hydroxide are typical examples. Acids and bases may also be classified according to the number of (H~+) ions they can donate per molecule. If an acid can donate only one (H~+) ion, it is known as monofunctional. If the available H~+ ions are more than one, a di- (two) or tri- (three) classification is used.