pH METER pH pH is an abbreviation of the French word “pouvoir hydrogene” that represents “hydrogen power” and was proposed by the Danish scientist Soren Peter Lauritz Sorensen in 1909 in order to express the very small concentrations of hydrogen ions. The pH is defined as the negative log of hydrogen ion activity. It does not indicates the hydrogen ion concentration. pH = - log (H + ) pH is an important parameter because many of nature's processes are highly dependent on pH. However, as most chemical and biological reactions are governed by the hydrogen ion activity. Every aqueous solution can be measured to determine its pH value. This value ranges from 0 to 14 pH. Values below 7 pH exhibit acidic properties. Values above 7 pH exhibit basic (also known as caustic or alkaline) properties. Since, 7 pH is the center of the measurement scale, it is neither acidic nor basic, it is called "neutral." pH MEASUREMENT pH in an aqueous solution can be measured in a variety of w