Which substance is amphiprotic?

Which substance is amphiprotic?

• A. Water
• B. Ammonia
• C. Hydrochloric acid
• D. Sulfuric acid

Answer: (A)

Amphiprotic substances can both donate and accept a proton in Brønsted–Lowry acid–base chemistry. Water does this naturally: it can donate a proton to form hydroxide (H2O ⇌ H+ + OH−) and it can also accept a proton to form the hydronium ion (H2O + H+ → H3O+). In pure water, autoionization shows both processes happening, keeping the solution neutral. Among the options, water is the only one that routinely acts as both an acid and a base in aqueous solution; the others are primarily acid or base in behavior. Therefore, water is amphiprotic.

Amphiprotic substances can both donate and accept a proton in Brønsted–Lowry acid–base chemistry. Water does this naturally: it can donate a proton to form hydroxide (H2O ⇌ H+ + OH−) and it can also accept a proton to form the hydronium ion (H2O + H+ → H3O+). In pure water, autoionization shows both processes happening, keeping the solution neutral. Among the options, water is the only one that routinely acts as both an acid and a base in aqueous solution; the others are primarily acid or base in behavior. Therefore, water is amphiprotic.