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In chemistry, hydronium (hydroxonium in traditional British English) is the cation [H 3 O] +, also written as H 3 O +, the type of oxonium ion produced by protonation of water.It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton (a positive hydrogen ion, H +) to the surrounding water molecules (H 2 O).
If an impurity is an acid or base, this will affect the concentrations of hydronium ion and hydroxide ion. Water samples that are exposed to air will absorb some carbon dioxide to form carbonic acid (H 2 CO 3 ) and the concentration of H 3 O + will increase due to the reaction H 2 CO 3 + H 2 O = HCO 3 − + H 3 O + .
Protons tunnel across a series of hydrogen bonds between hydronium ions and water molecules.. The Grotthuss mechanism (also known as proton jumping) is a model for the process by which an 'excess' proton or proton defect diffuses through the hydrogen bond network of water molecules or other hydrogen-bonded liquids through the formation and concomitant cleavage of covalent bonds involving ...
When a strong acid is dissolved in water, it reacts with it to form hydronium ion (H 3 O +). [2] An example of this would be the following reaction, where "HA" is the strong acid: HA + H 2 O → A − + H 3 O + Any acid that is stronger than H 3 O + reacts with H 2 O to form H 3 O +. Therefore, no acid stronger than H 3 O + exists in H 2 O.
An example is the H 2 O (water) molecule, which can gain a proton to form the hydronium ion, H 3 O +, or lose a proton, leaving the hydroxide ion, OH −. The relative ability of a molecule to give up a proton is measured by its pK a value. A low pK a value indicates that the compound is acidic and will easily give up its proton to a base.
Thus, the ammonium ion, NH + 4, in liquid ammonia corresponds to the hydronium ion in water and the amide ion, NH − 2 in ammonia, to the hydroxide ion in water. Ammonium salts behave as acids, and metal amides behave as bases. [10] Some non-aqueous solvents can behave as bases, i.e. accept protons, in relation to Brønsted–Lowry acids.
The hydroxides OH − that approach the anode mostly combine with the positive hydronium ions (H 3 O +) to form water. The positive hydronium ions that approach the cathode mostly combine with negative hydroxide ions to form water. Relatively few hydroniums/hydroxide ions reach the cathode/anode. This can cause overpotential at both electrodes.
The reaction is consistent with the Brønsted–Lowry definition because in reality the hydrogen ion exists as the hydronium ion, so that the neutralization reaction may be written as H 3 O + + OH − → H 2 O + H 2 O. When a strong acid is neutralized by a strong base there are no excess hydrogen ions left in the solution.