Acid–base models – Arrhenius, Brønsted–Lowry and Lewis, conjugate pairs
ChemistryAcids, Bases & TitrationAges 16–17
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Pick a reaction (HCl + H₂O, NH₃ + H₂O, CH₃COOH + NH₃, HCO₃⁻ + H₂O, HCl + NH₃ as gases, BF₃ + NH₃, Cu²⁺ + NH₃ and more) and watch it under the Arrhenius model (H⁺ or OH⁻ ions released in water), the Brønsted–Lowry model (a proton moves from acid to base, each conjugate acid–base pair in its own colour) and the Lewis model (an electron pair donated into an empty orbital). In the sorting game, label every species, choose the models that describe the reaction and find the amphiprotic species.
Lesson: Brønsted–Lowry acids and bases and conjugate pairs, compared with the Arrhenius and Lewis models
What it shows
Chemists have used three definitions of acids and bases. Arrhenius: in water an acid releases H⁺ ions and a base releases OH⁻ ions. Brønsted–Lowry: an acid donates a proton and a base accepts it, so every reaction forms a conjugate base and a conjugate acid; it also works without water. Lewis: a base donates a lone pair of electrons and an acid accepts it into an empty orbital, which covers BF₃ and metal ions. Each wider model includes the narrower ones. The circles stand for whole molecules or ions, and the positions of equilibria are not shown.
How to use
On Reaction animation, choose a Reaction and a Model, then press Run to watch the proton or the electron pair move; the table lists each species' role and conjugate partner. Switch the Model for the same reaction to compare. On Sorting game, tap each species to cycle its label, press the model buttons that describe the reaction, then Check and Next; the last round asks for the amphiprotic species.
Parameters you can change
- Screen Reaction animation, Sorting game
- Reaction HCl + H₂O, NH₃ + H₂O, CH₃COOH + NH₃, HCO₃⁻ + H₂O (HCO₃⁻ as a base), HCO₃⁻ + H₂O (HCO₃⁻ as an acid), HSO₄⁻ + H₂O, H₂O + H₂O (self-ionisation), HCl + NH₃ (gases), H₃O⁺ + OH⁻ (neutralisation), BF₃ + NH₃, Cu²⁺ + 4NH₃
- Model Arrhenius, Brønsted–Lowry, Lewis
Questions to explore
- Why can the Brønsted–Lowry model explain that ammonia is a base, while the Arrhenius model cannot?
- In H₃O⁺ + OH⁻ → 2H₂O, which species is each water molecule the conjugate of?
- Why is BF₃ a Lewis acid but not a Brønsted–Lowry acid?
