pH

The ph is a measure that indicates the hydrogen ion concentration of a solution, a measure of the solution’s acidity. Hydrogen ions are usually represented by the symbol H+. The term is defined as the negative logarithm of the concentration of H+ ions:

pH = -log10[H+] Equation 2.1

Where [H+] is the concentration of H+ ions in moles per liter. Because H+ ions associate with water molecules to form hydronium (H3O+) ions, pH also is often expressed in terms of the concentration of hydronium ions. If acid is added to water, however, an excess of H3O+ ions is formed: H+ (acid) + H2O (water) yields H3O+ (hydronium ions). When the concentration of H3O+ exceeds the concentration of OH-, the solution becomes acidic. In an acidic solution, the concentration of hydronium (H3O+) ions can range from 1 to 1 x 10-6 moles/liter, depending on the strength and amount of the acid. Therefore, acid solutions have a pH ranging from 6 (weak acid) to 0 (strong acid). Inversely, when the concentr...