A saturated solution of o-nitrophenol has PH=4.53. Calculate its solubility. PKa=7.23

C₆H₅NO₃----> C₆H₄NO₃^- + H⁺

                                    x                       x

lets solubility be x

so P^H = 4.53 or [H⁺] = 10^-4.53  so x = 10^-4.53

P^Ka = 7.23 or [H⁺] = 10^-7.23

K_a = [C₆H₄NO₃^-] [H⁺]   

[C₆H₄NO₃^-] = K_a / [H⁺]
                           = 10 ^-7.23+4.53

                        solubility   = 2x10^-3 g/L