Calculate the pH of the following solutions using the thermodynamic values of Ka given in Table 7.2

a.) 1*10^-3 benzoic acid, 0.1 M NaCl (Ka= 4.2)

b.) 1*10^-4 sodium Formate. 0.05 M MgCl2 (Ka=3.74)

c.) 1*10^-4 hydrogen sulfide, 0.024 M Na2SO4 (Ka1=7.02 Ka2= 17.4)