What kinds of ions do acids and bases form in water?       

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Acids produce hydrogen ions, H+, in water. Bases produce hydroxide ions, OH-.

A hydrogen ion is a bare proton that associates with a water molecule so the H+ ions produced by an acid exist as H3O+ ions:

`H^+ + H_2O -> H_3O^+`

There are three accepted theories defining acids and bases:

1. The Arrhenius theory defines an acid as substance that dissociates to produce H+ ions in solution and a base as a substance that dissociates to produce OH- ions in solution, as per the answer to your question.

2. The Bronsted-Lowery theory defines an acid as a proton donor and a base as a proton acceptor. (Remember that a proton is the same as an H+ ion.)

3. The Lewis theory defines an acid as an electron pair acceptor and a base as an electron pair donor.

Here are a few examples of these definitions:

HCl is both an Arrhenius acid and a Bronsted-Lowry acid. It dissociates to produce hydrogen ions in aqueous solution, and it donates a proton to a base. These are two different ways of describing the same behavior.

Bases that contain the hydroxide ion OH- are both Arrhenius and Brønsted-Lowry bases because they dissociate to produce OH- ions that "accept" or bond to protons:

`H^+ + OH^(-) -> H_2O`

H+ is a Lewis acid because it will "accept" or share a non-bonding pair of electrons on another atom or ion. For example, it accepts an electron pair from the Lewis base F-:

`H^+ + F^(-) -> HF`

Ammonia, NH3, is an example of all three types:

`NH_3 + H_2O --gt NH_4^+ + OH^-`

Ammonia produces OH- by reacting with water. It can also be said that it accepts a proton from water and that it donates an electron pair to an H+ ion.

Approved by eNotes Editorial Team
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