Brønsted–Lowry Acids & Bases
- The Brønsted-Lowry Theory defines acids and bases in terms of proton transfer between chemical compounds
- A Brønsted acid is a species that can donate a proton
- For example, hydrogen chloride (HCl) is a Brønsted acid as it can lose a proton to form a hydrogen (H+) and chloride (Cl-) ion
HCl (aq) → H+ (aq) + Cl- (aq)
- A Brønsted base is a species that can accept a proton
- For example, a hydroxide (OH-) ion is a Brønsted base as it can accept a proton to form water
OH- (aq) + H+ (aq) → H2O (l)
Conjugate acid-base pairs
- Conjugate acid-base pairs are a pair of reactants and products that are linked to each other by the transfer of a proton
- In a reaction equilibrium, the products are formed at the same rate as the reactants are used
CH3COOH (aq) + H2O (l) ⇌ CH3COO- (aq) + H3O+ (aq)
acid base conjugate base conjugate acid
- The reactant CH3COOH is linked to the product CH3COO- by the transfer of a proton from the acid to the base
- Similarly, the H2O molecule is linked to H3O+ ion by the transfer of a proton
- These pairs are therefore called conjugate acid-base pairs
- Conjugate here means related
- In other words, the acid and base are related to each other by one proton difference