Ion product

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The ion product is the product of the molar concentrations (or more precisely the activities ) of all ions dissolved in a medium (e.g. water ) by electrolytic dissociation . If it is a saturated solution, the ion product corresponds to the solubility product . If only ions produced by autoprotolysis are present in a system , the ion product corresponds to the autoprotolysis constant of the system.

Ion product of water

The ion product of pure water ( K W ) is particularly important . By autoprotolysis, water contains oxonium - (H 3 O + ) and hydroxide ions (OH - ):

For the ion product K W applies (with c ° = 1 ):

The activities of the two types of ions at 25 ° C are each 1.004 · 10 −7 , the ion product is 1.008 · 10 −14 , which roughly corresponds to the numerical product of the concentrations:

These variables determine the scale and the neutral value of the pH value , which is the negative decadic logarithm of the oxonium ion concentration:

See also