H

Hydronium Ion

H₃O⁺; formed: H₂O + H⁺ → H₃O⁺; Ka(H₃O⁺) = 55.5 M (approx.)
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Quick Reference
Formula / NotationH₃O⁺; formed: H₂O + H⁺ → H₃O⁺; Ka(H₃O⁺) = 55.5 M (approx.)
Also Known AsH₃O⁺, oxonium ion, protonated water, Zundel cation (H₅O₂⁺)

What is Hydronium Ion?

The H₃O⁺ ion formed when a proton (H⁺) is transferred to a water molecule. In aqueous solution, free protons do not exist; they are always associated with water as hydronium ions. The concentration of hydronium ions determines the pH of an aqueous solution.

Formula & Notation

H₃O⁺; formed: H₂O + H⁺ → H₃O⁺; Ka(H₃O⁺) = 55.5 M (approx.)

Other Names / Synonyms: H₃O⁺, oxonium ion, protonated water, Zundel cation (H₅O₂⁺)

Properties & Characteristics

The hydronium ion (H₃O⁺, also called oxonium ion) is the species formed when a proton (H⁺) bonds to a water molecule via a coordinate bond. It is the dominant form of the proton in aqueous solution. pH = −log[H₃O⁺]. In more accurate models, the proton is further hydrated as H₅O₂⁺, H₇O₃⁺, etc. The hydronium ion is a strong acid (fully dissociates in the Brønsted sense — it donates its extra proton to water in equilibrium with H₂O).

Uses & Applications

The hydronium ion is the relevant acid species in all aqueous acid-base chemistry, pH calculations, and titration analysis. It participates in all acid-catalysed reactions in aqueous media. Understanding hydronium ion formation is fundamental to understanding acid dissociation, buffer chemistry, and proton transfer mechanisms.

Safety Information

High hydronium ion concentration (low pH) in concentrated acid solutions is corrosive to skin, eyes, and respiratory tract. Acidic solutions that generate H₃O⁺ rapidly (strong acids) are more corrosive than weak acids at the same formal concentration. Always use appropriate PPE when working with acidic solutions.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Hydronium Ion
Formula H₃O⁺; formed: H₂O + H⁺ → H₃O⁺; Ka(H₃O⁺) = 55.5 M (approx.)
Index All "H" terms
Synonyms H₃O⁺, oxonium ion, protonated water, Zundel cation (H₅O₂⁺)

Frequently Asked Questions

The H₃O⁺ ion formed when a proton (H⁺) is transferred to a water molecule. In aqueous solution, free protons do not exist; they are always associated with water as hydronium ions. The concentration of hydronium ions determines the pH of an aqueous solution.

More "H" Terms

1-Hexanol C6H14O 2-Hydroxyethyl methacrylate C6H10O3 4-Hydroxybenzaldehyde C7H6O2 Haber Process N₂ + 3H₂ ⇌ 2NH₃ | ΔH = −92 kJ/mol Hafnium Hf Half Cell Half Life Half-Cell E = E° − (RT/nF)lnQ Half-Life A(t) = A₀e^(−λt); t½ = ln2/λ Half-Reaction Halide X⁻ (e.g., F⁻, Cl⁻, Br⁻, I⁻) Halogen F₂, Cl₂, Br₂, I₂, At; Group 17; ns²np⁵ valence configuration
View all "H" terms →
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Editorial standards: Chemical data is sourced from peer-reviewed literature, CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA, and IAEA. For educational purposes only — always consult official SDS documentation and qualified professionals before handling chemicals.

AllChemicals.info — The Online Chemical Glossary | https://allchemicals.info/chemical/508-hydronium-ion

For educational purposes only. Verify all information before use.