Consider the following reaction:
HC2H3O2(aq) + H2O(l) ⇌ H3O+(aq) + C2H3O−2(aq)
Kc = 1.8×10−5 at 25∘C
If a solution initially contains 0.230 M HC2H3O2, what is the equilibrium concentration of H3O+ at 25∘C?
Express your answer using two significant figures.