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Transfer of a hydrogen ion between molecules of the same substance, e. g. the autoprotolysis of methanol (2 CH 3 OH = CH 3 OH 2 + + CH 3 O - ). Autoprotolysis of water into hydronium ions and hydroxide ions results in equilibrium concentrations that satisfy K w = [H 3 O + ][OH - ], where the autoprotolysis constant K w is equal to 1.01 × 10 -14 at 25°C.