Concept confirmation about acid

Firstly, why OH–(aq) ion in an acid solution ?

In any aqueous solution, the water molecules undergoes self-ionization to give H+(aq) and OH-(aq) ions. The reaction is reversible.
H2O(l) = H+(aq) + OH-(aq)

Denote [H+(aq)] and [OH-(aq)] as the concentrations of H+(aq) and OH-(aq) ions.
Chemists have found that the product of [[H+(aq)] x [OH-(aq)] is equal to 1 x 10-14 (mol dm-3)2.

For example, in 1 M HCl :
[H+(aq)] = 1 mol dm-3
[OH-(aq)] = (1 x 10-14)/1 = 1 x 10-14 mol dm-3

You will learn the above topic in AL Chemistry.

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Secondly, if the concentrations of HCl(aq) in high enough, some H+(aq) and OH-(aq) ions would combine to give HCl molecules In other words, HCl molecules would also exist in concentrated hydrochloric acid.

2007-03-11 00:51:29 補充：
deionize 是「去離子」的意思，是用 deionizer （去離子器）把水變成較純淨的 deionized water （去離子水）。deionize 與題目無關。