Question

Write the modern definition of acid and base. Explain it by giving one example of each.

Answer 1

Compounds can be identified as acid or base by using the pH meter, i.e., if the pH is low then it is acid and if the pH is high then it is a base. Earlier the acids and base were based on the presence of hydrogen ions and hydroxyl ions present in the molecule, but the modern definition is based on the electron pair.

Complete answer:
There are three types of compounds, i.e., acids, bases, and neutral. Compounds can be identified as acid or base by using the pH meter, i.e., if the pH is low which lies between 0 – 6.9 then, it is acid and if the pH is high which lies between 7.1 – 14 then, it is a base, and the neutral compound has pH 7.
There were many theories used to explain the acids and bases but all the theories have some limitations. Earlier the acids and base were based on the presence of hydrogen ions and hydroxyl ions respectively present in the molecule.
But the modern definition of acids and bases is based on the movement of pairs of electrons, the acids are defined as a species that can accept a pair of electrons while the base is defined as a species that can donate a pair of electrons.
For example, $B{{F}_{3}}$ is an acid because there is a vacant orbital in boron, so it can accept a pair of the electron, $:N{{H}_{3}}$ is a base because there is lone pair of electrons on the nitrogen which can be donated. They combine with each other, the reaction is given below:
${{F}_{3}}B+:N{{H}_{3}}\to {{F}_{3}}B\leftarrow N{{H}_{3}}$

Note:
Water is a substance that can act as acid as well as a base in many reactions based on the conditions of the reaction and the pH of water is exactly 7 and doesn't give any change in the pH paper.