pH is a unit of measure that describes the acidity or alkalinity of a solution.
It is measured on a scale from 0 to 14. p in the pH term; They are derived from the mathematical symbol for minus logarithm, and H from the chemical formula of hydrogen. The definition of pH can be given as the minus logarithm of the hydrogen concentration:
pH = −log[H+]
pH provides the quantitative information needed by expressing the degree of acid or base in terms of the activity of the hydrogen ion. The pH value of a substance is directly dependent on the ratio of the hydrogen ion [H+] to the hydroxyl ion [OH−] concentration. If the H+ concentration is higher than the OH− concentration, the solution is acidic; that is, the pH value is lower than 7. If the OH− concentration is higher than the H+ concentration, our substance is basic; that is, the pH value is greater than 7. If equal amounts of OH− and H+ ions are present, the substance is neutral with a pH of 7.
Acids and bases each have free hydrogen and hydroxyl ions. Since the relationships of hydrogen and hydroxyl ions are constant under certain conditions and in a particular solution, it is possible to detect one by knowing the other. In this sense, pH is a measure of both alkalinity and acidity, although by definition it is a selective measure of hydrogen ion activity. Since pH is a logarithmic function, one unit change in pH corresponds to a ten-fold change in hydrogen ion concentration.
