(potentia hydrogenii - „Stärke des Wasserstoffs“, „power of hydrogen“)
It declares the concentration of hydrogen ions in a solution and is defined as the negative decadic logarithm of hydrogen ion concentration.
pH and concentration
pH = -lg [H+]
Annotation: [H+] is the symbol for the hydrogen ion concentration.
[H+] , pH
when the solution of a hydrogen ion concentration amounts e.g. , then the pH value is 3.
- pH < 7 signifies an acid solution (on a scale of 0 to 14)
- pH = 7 signifies a neutral solution
- pH > 7 signifies an alkaline solution (on a scale of 0 to 14)
So, the closer the pH to the pH of 7, the lower the strength of the acid or the alkali respectively.
- ordinary hydrochloride acid has the pH value of 0 (acid).
- ordinary potassium hydrochloride solution has the pH value of 14 (alkali).