Ionic Equilibrium

Concepts of Acids and Bases

Arrhenius Concept
According to Arrhenius, an acid is a substance that contains hydrogen and releases hydrogen ions (H+) in aqueous solution. A base is a substance that produces OH(aq).

In aqueous solution NH3 forms NH4OH which furnishes OH(aq),
The strength of an acid is defined in terms of concentration of H+(aq) that is present in the aqueous solution of a given concentration of the acid. Similarly the strength of a base depends upon the relative concentration of OH−(aq) in aqueous solution of the base. In neutralisation reaction, H + and OH ions combine to form water.

Bronsted Lowry’s Protonic Concept
Bronsted acid is a proton donor and Bronsted base is proton acceptor. The reaction of an acid with a base involves the transfer of proton from the acid to the base. Acids and bases exist in a solution in a state of dynamic equilibrium. The conjugate base of a Bronsted acid (HA) is the base that is formed when the acid has donoted a proton. The conjugate acid of a Bronsted base is the acid that is formed when the base has accepted a proton.
Lewis Acids and Bases
Lewis acid is a species that is capable of accepting a pair of electrons to form covalent bond and Lewis base is a substance that is capable of donating an electron pair to form a covalent bond.
Some examples of Lewis acid: BF3, Cu2+, Fe3+, SO2, SnCl2
Some examples of Lewis bases: F , NH3, CN , OH etc.

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