4. Acid-Base Reactions

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+.

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