Question

Write chemical reactions to show amphoteric nature of water.

Answer 1

Hint: Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms. A species that has the potential to act both as an acid and as a base according to Bronsted-Lowry Theory is said to be amphoteric.

Complete step by step answer:
Bronsted-Lowry Theory: This theory states that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.
The water molecule has hydrogen atoms and, therefore, could act as an acid in a reaction. The oxygen atom in the water molecule has two lone pairs, one of which could be used to form a bond with a proton and, therefore, the water molecule could act as a base in a reaction. Since water has the potential to act both as an acid and as a base, water is amphoteric.
The amphoteric nature of water is represented by the following chemical reactions.
Water as a base:
\[{H_2}O(l) + {H_2}S(g)\overset {} \leftrightarrows {H_3}{O^ + }(aq) + HS_{(aq)}^ - \]
Water as an acid:
\[{H_2}O(l) + N{H_3}(aq)\overset {} \leftrightarrows O{H^ - } + NH_4^ + \]
Self-ionization of water in which water simultaneously acts as acid and base.
\[2{H_2}O \to {H_3}{O^ + } + O{H^ - }\]

Note: Water plays an important role in the world economy. Approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and freshwater bodies is a major source of food for many parts of the world. The amphoteric nature of water can be used in industrial purposes widely.