Step 1: Understanding the Concept:
An amphoteric (or amphiprotic) substance is one that can act as both a Bronsted-Lowry acid (proton donor) and a Bronsted-Lowry base (proton acceptor).
Step 3: Detailed Explanation:
Water exhibits amphoteric behavior depending on the chemical environment:
1. As a Base: When reacting with an acid stronger than itself (like \(HCl\)), water accepts a proton to form the hydronium ion (\(H_3O^+\)).
\[ HCl(aq) + H_2O(l) \rightarrow H_3O^+(aq) + Cl^-(aq) \]
2. As an Acid: When reacting with a base (like \(NH_3\)), water donates a proton to form the hydroxide ion (\(OH^-\)).
\[ NH_3(aq) + H_2O(l) \rightarrow NH_4^+(aq) + OH^-(aq) \]
Step 4: Final Answer:
Water is amphoteric because it can donate protons to bases and accept protons from acids.