Everything about Acid-base totally explained
An
acid-base reaction is a
chemical reaction that occurs between an
acid and a
base. Several concepts exist which provide alternative definitions for the reaction mechanisms involved and their application in solving related problems. Despite several similarities in definitions, their importance becomes apparent as different methods of analysis when applied to acid-base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. Historically, the first of these scientific concepts of acids and bases was provided by the
French chemist Antoine Lavoisier, circa
1776.
Common acid-base theories
Lavoisier definition
Since Lavoisier's knowledge of
strong acids was mainly restricted to
oxyacids, which tend to contain central atoms in high
oxidation states surrounded by oxygen, such as
HNO3 and
H2SO4, and since he wasn't aware of the true composition of the hydrohalic acids, HCl, HBr, and HI, he defined acids in terms of their containing
oxygen, which in fact he named from Greek words meaning "acid-former" (from the
Greek οξυς (
oxys) meaning "acid" or "sharp" and γεινομαι (
geinomai) or "engender"). The Lavoisier definition was held as absolute truth for over 30 years, until the 1810 article and subsequent lectures by
Sir Humphry Davy in which he proved the lack of oxygen in
H2S,
H2Te, and the
hydrohalic acids.
Liebig definition
This definition is proposed by
Justus von Liebig circa
1838, based on his extensive works on the chemical composition of
organic acids. This finished the doctrinal shift from oxygen-based acids to hydrogen-based acids, started by Davy. According to Liebig, an acid is a hydrogen-containing substance in which the hydrogen could be replaced by a metal. Liebig's definition, while completely empirical, remained in use for almost 50 years until the adoption of the Arrhenius definition.
Arrhenius definition
The Arrhenius definition of acid-base reactions is a more simplified acid-base concept devised by
Svante Arrhenius, which was used to provide a modern definition of bases that followed from his work with
Friedrich Wilhelm Ostwald in establishing the presence of ions in aqueous solution in
1884, and led to Arrhenius receiving the
Nobel prize in chemistry in
1903 for "
recognition of the extraordinary services ... rendered to the advancement of chemistry by his electrolytic theory of dissociation" be used in favor of the older accepted term "oxonium" to illustrate reaction mechanisms such as those defined in the Brønsted-Lowry and solvent system definitions more clearly, with the Arrhenius definition serving as a simple general outline of acid-base character, which leads to the definition that in Arrhenius acid-base reactions, a salt and water is formed from the reaction between an acid and a base -- In contrast to the Arrhenius definition, the Brønsted-Lowry definition refers to the products of an acid-base reaction as conjugate acids and bases to refer to the relation of one proton, and to indicate that there has been a reaction between the two quantities, rather than a "formation" of salt and water, as explained in the Arrhenius definition. and not the removal of a proton from the nucleus of an atom, which would require inordinate amounts of energy not attainable through the simple dissociation of acids. In differentiation from the
Arrhenius definition, the Brønsted-Lowry definition postulates that for each acid, there's a conjugate acid and base or "
conjugate acid-base pair" that's formed through a complete reaction, which also includes water, which is
amphoteric: is an encompassing theory to the Brønsted-Lowry and solvent-system definitions and spans both aqueous and non-aqueous reactions. in
1939, further improved by
Håkon Flood circa
1947 and now commonly used in modern
geochemistry and
electrochemistry of molten salts, describes an
acid as an oxide ion acceptor and a
base as an oxide ion donor. For example:
» MgO (base) + CO
2 (acid) → MgCO
3
CaO (base) + SiO
2 (acid) → CaSiO
3 » NO
3- (base) + S
2O
72- (acid) → NO
2+ + 2SO
42-
Pearson definition
In
1963 Ralph Pearson proposed an advanced qualitative concept known as
Hard Soft Acid Base principle, later made quantitative with help of
Robert Parr in
1984. 'Hard' applies to species which are small, have high charge states, and are weakly polarizable. 'Soft' applies to species which are large, have low charge states and are strongly polarizable. Acids and bases interact and the most stable interactions are hard-hard and soft-soft. This theory has found use in both organic and inorganic chemistry.
Further Information
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