To determine the equilibrium concentration of hydronium ions in the solution, we use the given value of the percent ionized. Percent ionized is the percent of the ions that is dissociated into the solution. It is equal to the concentration of an ionized species over the initial concentration of the compound multiplied by 100 percent. For this case, the dissociation of the weak acid has a 1 is to 1 ratio to the ionized species such that the concentration of the CH3COO- and H+ ions at equilibrium would be equal. We calculate as follows:
5.2% = 5.2 M H3O+ / 100 M CH3COOH
5.2 M H3O+ / 100 M CH3COOH = [H3O+] / 0.048 M CH3COOH
[H3O+] = 0.2496 M
