Question

Explain amphoteric nature of water.

Hint:

The self-ionization of water \(H_2O + H_2O \rightleftharpoons H_3O^+ + OH^-\) is the most basic demonstration of its amphoteric nature.

Answer 1

Step 1: Understanding the Concept:
Amphoteric substances are those that can react as both acids (proton donors) and bases (proton acceptors) depending on the reacting species.
Step 2: Detailed Explanation:
1. Water as a base: When water reacts with a stronger acid like \(HCl\), it accepts a proton.
\[ HCl(aq) + H_2O(l) \rightarrow H_3O^+(aq) + Cl^-(aq) \]
2. Water as an acid: When water reacts with a base like \(NH_3\), it donates a proton.
\[ NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq) \]
Since water behaves as an acid in the presence of bases and as a base in the presence of acids, it is described as amphoteric or amphiprotic.
Step 3: Final Answer:
The ability of water to donate or accept protons makes it amphoteric.