Background[edit]
Svante Arrhenius defined an acid as a substances that produces hydrogen ions, or protons (H+
) in aqueous solutions. Hydrochloric acid (HCl) and sulfuric acid (H
2SO
4) are common examples of Arrhenius acids because, when they dissociate into their ions, they increase the amount of H+ in the solution:
HCl → H+
(aq) + Cl−
(aq)
H
2SO
4 → H+
(aq) + HSO−
4(aq)
Arrhenius defined a base as a substance that produces hydroxide (OH−
) in aqueous solutions. Arrhenius's definition of a base was limited because along with produced hydroxide ions in solution, the base must contain the hydroxide group in its formula. Potassium hydroxide (KOH) and caesium hydroxide (CsOH) are common examples of Arrhenius bases because, when they dissociate into their ions, they increase the amount of OH- in the solution:
KOH(aq) → K+
(aq) + OH−
(aq)
CsOH(aq) → Cs+
(aq) + OH−
(aq)
Net ionic equation[edit]
When an acid reacts with an equal amount of a base, the word "neutralization" is used to describe the result because the acid and base properties of H+ and OH- are destroyed or neutralized. In the reaction, H+ and OH- combine to form HOH - more commonly written as H2O, the water molecule. Thus, acid–base neutralization reactions can be simplified to the net ionic equation:
H+
+ OH− → H
2O
It is important to realize that this representation is somewhat inaccurate, as it is known that the hydrogen ion (H+) does not actually occur by itself, but instead as the hydronium ion (H3O+). As seen in the following reaction, the H+, or protons, cause molecules of water undergo protonation to form the hydronium ion:
H+ + H2O → H3O+
Considering the hydronium ion, the actual net ionic reaction occurring is:
H3O+ + OH- → 2H2O
General neutralization equation[edit]
A neutralization reaction is a type of double replacement reaction. Typically, the resulting solution produced by the reaction consists of a salt and water. The general formula for acid–base neutralization reactions can be written as acid + base → salt + water
HA + BOH → BA + H2O where HA represents the Arrhenius acid, BOH represents the Arrhenius base, and BA is the salt produced. Notice how, typical of a double replacement reaction, the cations and anions of the substances merely switch places.
An example reaction of this form is the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH):
NaOH + HCl → NaCl + H2O
Water and sodium chloride, or common table salt are produced.
The following are other examples of acid-base neutralization reactions
Sulfuric acid reacting with ammonium hydroxide to produce ammonium sulfate and water
H2SO4 + 2NH4OH → (NH4)2SO4 + 2H2O
Carbonic acid reacting with sodium hydroxide to produce sodium carbonate and water
H2CO3 + 2NaOH → Na2CO3 + 2H2O
Hydrochloric acid reacting with aluminium hydroxide to produce aluminium chloride and water
3HCl + Al(OH)3 → AlCl3 + 3H2O
Acid-alkali[edit]

An acid–alkali reaction is a neutralization reaction which is considered a special case of an acid–base reaction, where the base used is also