 Virtually all such free protons quickly react with water to form hydronium; acidity of an aqueous solution is therefore more accurately characterized by its hydronium concentration.In organic syntheses, such as acid catalyzed reactions, the hydronium ion () can be used interchangeably with the ion; choosing one over the other has no significant effect on the mechanism of reaction.Researchers have yet to fully characterize the solvation of hydronium ion in water, in part because many different meanings of solvation exist.