The Self-ionization of water reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Self-ionization of water

Self-ionization or autoionization of water is when water (H₂O) is dissociated into hydronium (H₃O⁺) and hydroxide (OH^-) ions.

Water, however pure, is not a simple collection of H₂O molecules. Sensitive equipment can detect a very slight electrical conductivity even in "pure" water, but according to the theories of Svante Arrhenius, conductivity must be due to the presence of ions. Researchers have theorized that that H₂O molecules will react with each other to form hydronium and hydroxide ions. The reaction is as follows:

There is normally a very low percentage of H₃O⁺ and OH^- in water. The equilibrium constant for pure water at 25°C is 10^-14, which means for every ten million (10⁷) molecules of water, one will autoionize. A water deionizer can recombine these naturally occurring ions into pure deionized water temporarily.

See Also:

• pH
• SATP
• Equilibrium

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