Advantages of Brønsted-Lowry Theory

The Brønsted-Lowry acid-base theory has several advantages over the Arrhenius theory. Recall that the Arrhenius theory defines an acid as any species that increases the concentration of H⁺/H₃O⁺ in solution. Consider the following reactions of acetic acid (CH₃COOH), the organic acid that gives vinegar its characteristic taste:

1. CH₃COOH + H₂O ⇌ CH₃COO^– + H₃O⁺
2. CH₃COOH + NH₃ ⇌ CH3COO^– + NH₄⁺

Both theories easily describe the first reaction: CH₃COOH acts as an Arrhenius acid because it acts as a source of H₃O⁺ when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH₃COOH undergoes the same transformation, in this case donating a proton to ammonia (NH₃); this cannot be described using the Arrhenius definition of an acid, however, because the reaction does not produce H₃O⁺.