(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.

calculated example

Neutral solution:

[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).


schule/ch/bili/ph.txt · Zuletzt geändert: 2018/05/30 13:45 von ahrens
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