pH

A scale that expresses acidity or basicity (alkalinity), denoting the negative logarithm of the hydrogen-ion activity. The scale is from 0 to 14, with 7 representing a neutral basis at 25°C. The less a given solution is below 7, the more acidic it is; the greater it is above 7, the more basic it is. An increase of 1 in pH represents a 10 times decrease of acidity of the solution. Pure, neutral water has a pH of 7, so for pH above 7, an increase of 1 unit represents a 10 times increase in alkalinity. The pH level frequently is used to assess the efficiency of acids, such as those used for pickling.