Question

How would you identify the conjugate acid-base pairs in the equilibrium equation: HC2H3O2 + H2O --> H3O^+ + C2H3O2^-?

Answer 1

`H_3C-C(=O)OH(aq) +H_2O rightleftharpoons H_3C-C(=O)O^(-)(aq) +H_3O^+`

Explanation:

The conjugate base of acetic acid is the acetate anion (the parent acid less a proton, `H^+`), hence `H_3C-C(=O)O^(-)`. The conjugate acid of `OH_2` is water plus a proton, i.e. an hydronium ion, `H_3O^+`. This is a representation, and as far as anyone knows the hydronium ion is a cluster of 3-4 water molecules (say `O_3H_6`) plus a proton to give `H_7O_3^+`. To represent the reactivity of this species in aqueous solution, `H^+` or `H_3O^+`, are entirely appropriate shorthands.