Theories of acids and bases
2 marks · HardState and describe one key difference between the Arrhenius and Bronsted-Lowry theories of acids and bases.
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Arrhenius: acids produce H^+ and bases produce OH^- in aqueous solution. Bronsted-Lowry: acids are proton donors and bases are proton acceptors; this definition applies more broadly than just aqueous solutions.
Also accept: Arrhenius acids produce H^+ and bases produce OH^- only in water; Bronsted-Lowry acids donate protons and bases accept protons, covering more reactions than just those in solution.; Arrhenius definition is limited to aqueous solution; Bronsted-Lowry applies to more types of reactions.
Common mistakes: Describing only one theory, not both.; Confusing donor/acceptor roles.; Saying both are limited to aqueous reaction.
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Marking points
B1 · 1 mark · Correctly describes the Arrhenius definition (acids produce H^+, bases produce OH^- in aqueous solution).
B2 · 1 mark · Correctly describes the Bronsted-Lowry theory as proton transfer (acid = proton donor, base = proton acceptor), or explains the broader application.
Worked solution
Arrhenius theory states that acids produce H^+ ions and bases produce OH^- ions, but only in aqueous solution.
The Bronsted-Lowry theory states that acids are proton donors and bases are proton acceptors, and this applies to a wider range of situations, not just aqueous solutions.