Why is water often ignored in the autoionization of H2O?

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SUMMARY

Water is often ignored in the autoionization of H2O due to its high concentration of approximately 55M in aqueous solutions. This concentration remains relatively constant during reactions, allowing it to be treated as a constant in the equilibrium expression. The autoionization reaction can be represented as H2O + H2O ⇌ H3O+ + OH-, with the equilibrium constant Kc expressed as Kc = [H3O+][OH-]. This simplification is crucial for understanding the behavior of acids and bases in water.

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  • Understanding of chemical equilibrium concepts
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Homework Statement


i was wondering if anyone knows why water is ignored in the autoionization of water? thanks


Homework Equations


H2O+H2O= H3O+OH
Kc=[H][OH]


The Attempt at a Solution

 
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In an aqueous solution (i.e. a solution where water is the solvent), the concentration of water is about 55M. Any reactions that occur in water that use water as a reactant or product will not significantly change the concentration of water in the solution. Therefore, one can treat [H2O] as a constant that gets added into the equilibrium constant.
 

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