HAc + H2O = Ac- + H3O+ Ka=1.76*10^-5
Ka= [H3O+][Ac-]/[HAc] 设[H3O+]=[Ac-]=x mol/L
x^2/Ka = 0.10
x = (0.10*1.76*10^-5)^0.5 = 1.33*10^-3 mol/L