hydronium ion

chemical ion

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June 29, 2026

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A hydronium ion is a hydrated hydrogen ion, represented by the chemical formula H₃O⁺. Strictly speaking, a hydrogen ion (H⁺) is the nucleus of a hydrogen atom, which is a single proton. However, in water solutions, a bare proton is unstable and readily combines with water molecules.12

The hydronium ion is formed when a proton attaches to a water molecule (H₂O). The concentration of hydronium ions in a water solution is a measure of its acidity; a higher concentration indicates a more acidic solution and a lower pH.2

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acid–base reaction
The Brønsted–Lowry definition
The hydronium ion (H₃O⁺), which is the hydrogen ion in aqueous solution, also belongs to this class. The charge of these ionic acids, of course, always must be balanced by ions of opposite charges, but these oppositely charged ions usually are irrelevant to the acid–base properties…
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The hydronium ion (H₃O⁺), which is the hydrogen ion in aqueous solution, also belongs to this class. The charge of these ionic acids, of course, always must be balanced by ions of opposite charges, but these oppositely charged ions usually are irrelevant to the acid–base properties…
Read More