Hydronium ion

Hydronium ion and other acidic varieties in pure water. H+(aq) is used as an abbreviation because that hydronium.

An exceedingly essential feature the water is the it have the right to play the role of an mountain or a base, in regards to the Brønsted-Lowryacid-base definitions. Both functions of water deserve to be combinedinto a single equation (shown below) representing a complete Brønsted-Lowryacid-base reaction. This reaction have the right to be described as one autoionization the water. Keep in mind that in part sources, this is referred to as autoprotolysis, or autodissociation).


The products of this reaction room the 2 polyatomic ions, hydronium ion (H3O+), and hydroxide ion (OH−).This ionic equation is frequently abbreviated by chemistry by removed of a water molecule and letting H+(aq) stand for hydronium ion:

H2O(l) → H+(aq) + OH−(aq)

For the services of convenience, the H+(aq) abbreviation for hydronium ion is extensively used. To be clear, H+ itself would be just an isolated proton (for 1H) so it is necessary to note that no such varieties exists in aqueous solution. The species formed through H+ moved to a water molecule, H3O+ (the framework of i m sorry is shown at reduced right) best represents the acidic types in water.


In instances where strong acids are produced by reaction v water, such as as soon as hydrogen chloride, HCl(g) disappear in water, it reaction nearly fully with water according to the chemistry equation:

HCl(aq) + H2O(l) → H3O+(aq) + Cl−(aq)

The common abbreviated kind of this chemistry equation provides H+(aq) in location of hydronium, and also drops the water reactant indigenous the equation:

HCl(aq) → H+(aq) + Cl−(aq)

as soon as hydrochloric acid is written as HCl(aq), the is presume to stand for in ionic type H+(aq) and also Cl−(aq) (or H3O+(aq) and also Cl−(aq) in non-abbreviated form) together hydrochloric acid is a strong electrolyte.

We can quantify water"s small tendency come autoionize by specifying a special form of equilibrium constant called Kw and also assigning an experimentally determined value come it.

Kw = < H+ >< oh − > = 1.0 × 10−14 (at 25°C).

keep in mind that this is the equilibrium constant expression the we would certainly write because that the chemistry equation representing the autoionization reaction the water, considering the concentration that water as a constant. The very tiny value for Kw shows the an extremely weak propensity of water to autodissociate.

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learning objectives and questionsUnderstand the autoionization that water and also use Kw.