Theories of acids and bases
2 marks · NormalState two differences between the Arrhenius and Bronsted-Lowry theories of acids and bases.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
Also accept: Arrhenius theory: acid produces H^+ in water, base produces OH^-; Bronsted-Lowry: acid donates proton, base accepts proton; Arrhenius only works for aqueous reactions; Bronsted-Lowry applies to more reactions, including non-aqueous
Common mistakes: Mixing up which theory is the older/limited one; Mis-defining base in Arrhenius as only 'accepts protons'
Show mark scheme and worked solution
Marking points
B1 · 1 mark · One clear difference: e.g., Arrhenius restricted to aqueous, Bronsted-Lowry not.
B2 · 1 mark · Second clear difference: e.g., Arrhenius: acids produce H^+, bases produce OH^-; Bronsted-Lowry: acid is a proton donor, base proton acceptor.
Worked solution
1. The Arrhenius theory defines acids as substances that produce H^+ ions in aqueous solution and bases as those that produce OH^- ions in aqueous solution. The Bronsted-Lowry theory defines acids as proton donors and bases as proton acceptors, not limited to aqueous solutions.
2. The Arrhenius model is restricted to water as the solvent, while the Bronsted-Lowry definition applies to reactions occurring in any solvent or even in the gas phase.