-There have been many attempts to define the difference between acids and bases. The three main theories in use today are:
-Arrhenius defined acids and bases as follows:
Examples of acids:
Examples of bases: .
According to Arrhenius concept, carbon dioxide, sulphur dioxide, etc., are not regarded as acids and are not regarded as bases.
-Bronsted and Lowry proposed a concept of acids and bases, which are independent of solvent.
-According to this concept, acids and bases are defined as follows:
-An acid is a species (a molecule, a cation (or) an anion) capable of donating one or more protons to any other substance called Bronsted-Lowry acid.
-Bronsted acids dissociate to release protons, resulting in a higher concentration of H+ ions in the solution.
-Strong Bronsted-Lowry acids are those that have a strong inclination to donate a proton but have a weak conjugate base.
-Weak Bronsted-Lowry acids have a slight tendency to give a proton, while their conjugate base is strong.
Examples for acids:
-A base is a species (a molecule, a cation (or) an anion) capable of accepting one or more protons from an acid; such a base is called the Bronsted-Lowry base.
Examples for bases:
Therefore, an acid is a proton donor, and a base is a proton acceptor.
-A species with an empty orbital and hence the ability to take an electron pair.
-Lewis acids have electrophilic properties.
- are examples of Lewis acids.
-A Lewis acid absorbs an electron pair from a Lewis base, resulting in the formation of a coordinate covalent bond.
-A Lewis base is a species that has a single pair of electrons and hence can operate as an electron donor.
-Lewis bases have nucleophilic properties.
- are examples of Lewis bases.
For neutral solution, , For acidic solution, For basic solution,
-The other way to check if a substance is acidic or basic is by using a litmus paper. There exist two types of litmus paper available, used to identify the acids and bases. They are the red litmus paper and the blue litmus paper. The blue litmus paper changes red under acidic conditions, whereas the red litmus paper turns blue under alkaline or basic conditions.