The faradaic impedance for nitromethane reduction on mercury in aqueous solutions of different pH values in the range pH 2-8 is analyzed with the equations previously derived for an electron reduction followed by a chemical step mechanism with two diffusing intermediates (EC-C-E mechanism). The reaction parameters for the first one-electron reduction and for the second three-electron reduction an studied as a function of pH, The results can be explained if a branched mechanism including two parallel EC (electron reduction and chemical reaction) sequences is assumed for the first reduction and a CECee sequence for the second reduction. The use of an equivalent resistance circuit to deduce the kinetic equations for different possible branched mechanisms is presented.