Calculate [h3o+] for the 0.10 m ch3cooh solution which has a ph = 2.88. -what percent of the weak acid is dissociated?

The concentration of the hydronium ion can be calculated from the pH as follows:

pH = -log[H3O]
2.88 = -log [H3O]
[H3O] = 1.32x10^-3 M

The percent dissociation can be calculated as follows:

% dissociation = 1.32x10^-3 / 0.10 x100 = 1.32%

The mass has escaped into a gas which you can not see so the law stays true.