hydrogen ion scale


hydrogen ion scale

A scale used to express the degree of acidity or alkalinity of a solution. The classic pH scale extends from 0.00 (total acidity) to 14 (total alkalinity), the numbers running in inverse order of hydrogen ion (pH) concentration. The pH value is the negative logarithm of the hydrogen ion (pH) concentration of a solution, expressed in moles per liter.

As the hydrogen ion concentration decreases, a change of 1 pH unit means a 10-fold decrease in hydrogen ion concentration. Thus a solution with a pH of 1.0 is 10 times more acid than one with a pH of 2.0 and 100 times more acid than one with a pH of 3.0. A pH of 7.0 indicates neutrality. Very concentrated (> 1molar) mineral acids and bases go beyond the classic scale to values < 0.00 and > 14, respectively.

As the hydrogen ion concentration varies in a definite reciprocal manner with the hydroxyl ion (OH-) concentration, a pH reading above 7.0 indicates alkalinity. In the human body, arterial blood is slightly alkaline, having a normal pH range of 7.35 to 7.45.

 See: pHSee also: scale