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Acids and Bases: An Introduction |
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Autoionization of WaterIf water can act as an acid or base, can a water molecule react with another water molecule, one acting as a base and accepting a proton from the other? The chemical equation for this reaction would be: ![]() Since this reaction is an equilibrium, an equilibrium constant expression can be written:
The equilibrium constant for this reaction is called Kw.
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This equilibrium and the value of Kw allow you to calculate the concentration of either H3O+ or OH- if the concentration of the other is known. When [H3O+] and [OH-] are equal, the solution is said to be neutral. If [H3O+] is greater than [OH-], the solution is acidic and if [OH-] is greater than [H3O+], the solution is basic:
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