In this paper, we explore the effects of two organic additives (guar and a selectively hydrolyzed polyacrylamide) in the presence of chloride ions on copper electrodeposition using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) at a rotating cylinder electrode (RCE). This paper also demonstrates that the CV and EIS results are consistent and that the selectively hydrolyzed polyacrylamide, "activated polyacrylamide" (APAM), acts as a suppressor/inhibitor at the cathode/ electrolyte interface, whereas guar does not. This paper presents an EIS measurement model for the effect of APAM + Cl- on a copper cathode. The EIS model was applied to data obtained at a potential of -470 mV vs a mercurous-mercuric sulfate reference electrode (MSE) at 45 °C. A comparison between the effect of APAM + Cl- and guar + Cl- was conducted at -490 mV (vs MSE) at 45°C. APAM + Cl- was also investigated at -445 mV (vs MSE) at 65°C. EIS was used to determine the effect of APAM + Cl- or guar + Cl- aging on the charge-transfer resistance using the RCE. CV was used to determine their effect on the polarization of the electrode. The EIS and CV results are consistent.