PH
The term pH is a convenient way to express the concentration of hydrogen ions (H+) in an aqueous solution. The lower case p in pH stands for "power of" with H being the symbol for the element hydrogen. Mathematically, it is the -log of the concentration in molarity of hydrogen ions in a solution. For chemists, the term hydronium ion (H3O+ )is often substituted for hydrogen ion to reflect the association of a hydrogen ion with a molecule of water.
Water undergoes slight dissociation into hydrogen ions (H+) and hydroxyl ions (OH-). When the concentrations of these two ions are equal, the solution is considered neutral. If the concentration of hydrogen ions is larger than the concentration of hydroxl ions, the solution is acidic. If hydroxyl ions are in greater concentration, the solution is considered alkaline or basic. Pure water at room temperature will have a neutral pH of 7.00. Values of pH below 7.00 are found in acidic solutions while values above 7.00 characterize basic solutions.
The pH of natural rainwater is slightly acidic, around 5.6, because carbon dioxide dissolves in water and forms carbonic acid. Human blood has a pH of 7.3-7.5. Seawater has a pH of 7.8-8.3
The proper pH is important to life on Earth. The pH of a solution will affect mineral solubility, solubility and structure of organic molecules, and protein structure.