7.2.3—Brønsted–Lowry theory of acids and bases
- Syllabus
- 9701–2028–2029
- Objective
- 7.2.3
- Level
- AS
Conjugate acid–base pairs differ by one proton
A conjugate acid is formed when a base accepts a proton; a conjugate base is formed when an acid donates one. The members of a conjugate pair differ by exactly H⁺.
Label both proton transfers in the equation, not just the reactant called “acid” in everyday language.
In NH₃ + H₂O ⇌ NH₄⁺ + OH⁻, NH₃/NH₄⁺ is a conjugate base/acid pair and H₂O/OH⁻ is a conjugate acid/base pair.
Conjugate does not mean equal strength or identical charge. It means the formulas differ by one proton under the reaction conditions.
ConceptA-Level CAIE Chemistry AS