What is a conjugate acid–base pair? Provide an example.

What is a conjugate acid–base pair? Provide an example.

• A. H2CO3 and HCO3-.
• B. H2CO3 and CO3^2-.
• C. H2O and H3O+.
• D. NH3 and NH4+.

Answer: (A)

A conjugate acid–base pair is two species that differ by exactly one proton. An acid donates a proton and becomes its conjugate base, while that base can accept a proton to become its conjugate acid. In this example, carbonic acid (H2CO3) can donate one proton to form bicarbonate (HCO3−). Because H2CO3 and HCO3− are related by loss of a single H+, they form a conjugate acid–base pair: H2CO3 is the acid, and HCO3− is its conjugate base. Other options also illustrate the idea in different contexts: CO3^2− would require removing two protons from H2CO3, so it’s not a direct conjugate pair with H2CO3; H2O and H3O+ are a conjugate pair (water is the base, hydronium is the conjugate acid); NH3 and NH4+ are another valid conjugate pair (ammonia is the base, ammonium is the conjugate acid). The given example is a clear, textbook demonstration of the one-proton difference defining a conjugate acid–base pair.

A conjugate acid–base pair is two species that differ by exactly one proton. An acid donates a proton and becomes its conjugate base, while that base can accept a proton to become its conjugate acid.

In this example, carbonic acid (H2CO3) can donate one proton to form bicarbonate (HCO3−). Because H2CO3 and HCO3− are related by loss of a single H+, they form a conjugate acid–base pair: H2CO3 is the acid, and HCO3− is its conjugate base.

Other options also illustrate the idea in different contexts: CO3^2− would require removing two protons from H2CO3, so it’s not a direct conjugate pair with H2CO3; H2O and H3O+ are a conjugate pair (water is the base, hydronium is the conjugate acid); NH3 and NH4+ are another valid conjugate pair (ammonia is the base, ammonium is the conjugate acid). The given example is a clear, textbook demonstration of the one-proton difference defining a conjugate acid–base pair.