Self-ionization of water
= Self-ionization of water
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Two <water> <molecules> can exchange a <proton>, producing <hydronium> and <hydroxide> <ions>: $2\mathrm H_2\mathrm O\rightleftharpoons\mathrm H_3\mathrm O^++\mathrm{OH}^-$. Even pure <water> therefore supplies <ions>; extreme <dilution> eventually invalidates the <strong acid> assumption that it supplies all the <hydronium>.