Hydronium is what you get when you put water and hydrogen ions together, forming H3O+. Hydronium is the simplest form of oxonium, which is any ion that contains the trivalent oxygen cation. Hydronium is also known as hydroxonium. As with many species in chemistry, the nomenclature isn't the same everywhere.
Sources of Hydronium
Where would you find hydronium? Pure water auto-dissociates, so both hydronium and hydroxide ions exist in any aqueous solution. The ratio between hydroxide and hydronium ions may be used to calculate the solution's pH. The species occurs whenever an Arrhenius acid dissolves in water. Hydronium is found in interstellar clouds and in the tails of comets. Interstellar hydronium probably forms as a result of chemical reactions following the ionization of H2 into H2+. Research is ongoing to elucidate the nature of the reactions.
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