Knowledge database: Chemical equilibrium: pH value

In cases when the concentration of H⁺ is equal to the concentration of OH^- ions, we have a neutral solution. Acids are solutions in which the concentration of the hydrogen ions is higher than the concentration of hydroxide ions. Bases are solutions in which the concentration of the hydroxide ions is higher than the concentration of hydrogen ions. In practice, one will mostly encounter values from 10^-14 to 1 mol/dm³.

In order to make the expression of the hydrogen concentration simpler, a so called hydrogen exponent has been introduced. It is represented by the following formula:

pH = -log ( [H⁺] / mol dm^-3 )

By logarithming the values of hydrogen concentration, one can get values between 0 and 14 (image above). A lower value means that the acidity is higher and the alkalinity is lower. In the reverse case, a higher value means that the acidity is lower and that the alkalinity is higher.