What is the hydronium ion concentration of a 0.500 M acetic acid solution with Ka = 1.8 x 10-5? The equation for the dissociation of acetic acid is: CH3CO2H(aq) + H2O(l) <---> H3O+(aq) + CH3CO2-(aq)
A. 3.0 x 10-2 M
B. 4.2 x 10-2 M
C. 3.0 x 10-3 M
D. 4.2 x 10-3 M