Ionode IJ pH V5.1 Bedienungsanleitung PDF herunterladen (Seite 6)

Ionode IJ Instruction Manual 6

4. pH

4.1. Theory

pH is a scale of active hydrogen ion

concentration in aqueous solution. In pure

water, the concentration of hydrogen ions is

–7

M. The pH scale converts this to a

convenient positive number:

 

][log





apH

pH indicates acidity (pH<7), alkalinity (pH >7) or

neutrality (pH = 7).

Pure water undergoes autoprotolysis to yield

equal numbers of hydrogen and hydroxide ions:



 OHHOH

The equilibrium constant at 25

C is:

10][][



 OHHK

pOH is the negative logarithm of the active

hydroxide concentration. The equilibrium

expression can be rewritten as:

14 pOHpHpK

This equation applies for all aqueous systems.

Very strong acids and bases can have pH’s <0

and >14 respectively.

Although pH is defined for aqueous solutions,

measurements can be made in non-aqueous

solutions provided the solvent is sufficiently

conductive, or a conductive solvent is added to

a non-conductive sample.

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Ionode IJ pH V5.1 Bedienungsanleitung Seite 6