25.1.2—Conjugate acid–base pairs, identifying such
- Syllabus
- 9701–2028–2029
- Objective
- 25.1.2
- Level
- A2
Identify conjugate acid–base pairs by removing or adding one proton
In HA + B ⇌ A⁻ + BH⁺, HA/A⁻ and B/BH⁺ are conjugate pairs. Each pair differs by one H⁺ and the charges change accordingly.
Mark the proton donor and acceptor first, then pair each reactant with its product. This prevents confusing the acid with its conjugate acid.
HCO₃⁻ + H₂O ⇌ H₂CO₃ + OH⁻ contains HCO₃⁻/H₂CO₃ and H₂O/OH⁻ pairs; bicarbonate is amphiprotic.
Do not pair species that differ by two protons or by an unrelated atom.
ConceptA-Level CAIE Chemistry A2