53 of 57 Common ions Effect Calculate the pH of an aqueous solution that is both 1.00 M CH3COOH and 1.00 M CH,COONa CH,COONa(s)-â CH3COO-(aq) + Na"(aq) The reaction Initial concentrations, M Changes, M Equilibrium concentrations, M: (1.00 -x) 1.00 1.00 rt x1.00 + x) H3O CH3COO] Next, we write the Ka exession and substitute numerical values from our ICE table and the value of K, for acetic acid from Table 15.2 [CH3COOH]-ä¸= 1.8 à 10 = 1.8 à 10-5 Now let us assume that x is very small and that therefore (1.00 -x)~ (1.00+x 1.00 x(1.00) = 1.8 à 10-5 X = [H3O+] = 1.8 à 10-5 M 1.00 We calculate the pH from [H,O in the usual way pH =-log[H,O+] =-log( 1.8 x 10-5) = 4.74