• The Br?nsted-Lowry Theory?defines acids and bases in terms of proton transfer between chemical compounds
• A?Br?nsted acid?is a species that can donate a proton
  • For example, hydrogen chloride (HCl) is a Br?nsted acid as it can lose a proton to form a hydrogen (H+) and chloride (Cl-) ion

HCl (aq) → H+?(aq) + Cl-?(aq)

• A?Br?nsted base?is a species that can accept a proton
  • For example, a hydroxide (OH-) ion is a Br?nsted base as it can accept a proton to form water

  OH-?(aq) + H+?(aq) → H2O (l)

• 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