Safety boundary
Use virtual indicators or teacher-supervised food-safe indicator only. Never mix cleaners, household acids/bases, or unknown chemicals.
Explicit chemistry instruction
Arrhenius acids increase H3O+ in water and Arrhenius bases increase OH− in water.
Brønsted–Lowry expands the model: acids donate protons and bases accept protons.
Different models are useful at different scopes; a broader model can explain reactions beyond simple aqueous OH− production.
Vocabulary: acid; base; Arrhenius; Brønsted–Lowry; proton transfer.
Worked example
HCl donates a proton to water, forming H3O+; water acts as the proton acceptor/base.
Guided question
In NH3+H2O⇌NH4++OH−, which species acts as a Brønsted base?
Independent work
- Classify six species in supplied reactions.
- Compare Arrhenius and Brønsted labels.
- State one scope difference.
Instructional depth extension · acid–base model comparison
Use three models deliberately rather than treating “acid” and “base” as one fixed definition. In an Arrhenius model, acids increase hydronium and bases increase hydroxide in water. In the Brønsted–Lowry model, an acid donates a proton and a base accepts one. Lewis acid–base reasoning broadens the idea again to electron-pair acceptance and donation.
For HCl + H₂O → H₃O⁺ + Cl⁻, HCl donates H⁺ and H₂O accepts it. The conjugate pairs are HCl/Cl⁻ and H₂O/H₃O⁺. Labeling the pairs makes the transfer model testable rather than relying on memorized substance lists.
Model-limit check: choose the narrowest model that answers the question, and state when a broader model is needed.
Misconception check
An acid is not defined merely by containing H in its formula.
Formative check
What makes a Brønsted base?
Reveal response
It accepts a proton.
Mentor evidence conference
Ask Archaemenes to audit proton-transfer roles, conjugate-pair logic, and model scope.
Teacher guidance
Foundation: Use donor/acceptor arrows.
Core: Classify acids and bases in reactions.
Extended: Compare model scope and limitations.