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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).
Hydronium is one of a series of oxonium ions with the formula R n H 3−n O +.Oxygen is usually pyramidal with an sp 3 hybridization.Those with n = 1 are called primary oxonium ions, an example being protonated alcohol (e.g. methanol).
By definition, an acid is an ion or molecule that can donate a proton, and when introduced to a solution it will react with water molecules (H 2 O) to form a hydronium ion (H 3 O +), a conjugate acid of water. [4] For simplistic reasoning, the hydrogen ion (H +) is often used to abbreviate the hydronium ion.
Pure water containing no exogenous ions is an excellent electronic insulator, but not even "deionized" water is completely free of ions. Water undergoes autoionization in the liquid state when two water molecules form one hydroxide anion (OH −) and one hydronium cation (H 3 O +). Because of autoionization, at ambient temperatures pure liquid ...
The water molecule is amphoteric in aqueous solution. It can either gain a proton to form a hydronium ion H 3 O +, or else lose a proton to form a hydroxide ion OH −. [7] Another possibility is the molecular autoionization reaction between two water molecules, in which one water molecule acts as an acid and another as a base.
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.
Note that in solution H + exists as the hydronium ion H 3 O +, and further aquation of the hydronium ion has negligible effect on the dissociation equilibrium, except at very high acid concentration. Figure 2. Buffer capacity β for a 0.1 M solution of a weak acid with a pK a = 7
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.