Piezoelectric resonator and drag force measurements show a decrease of interfacial viscosity of perchlorate and chloride aqueous solutions during polarization of gold electrode towards potential of zero charge. Though more noisy, drag force measurements have the advantage over piezoelectric technique as the former is insensitive to potential dependent adsorption, which causes distortion of data on liquid properties obtained from piezoelectric resonator measurements at more positive potentials. The shift in the potential of the viscosity minimum, obtained from drag force measurements follows the shift in the potential of zero charge (pzc) with a change in concentration. In addition, the Esin-Markov relation holds at these potentials: tenfold increase in concentration of specifically adsorbing chloride shifts the potential of viscosity minimum by -46 mV, whereas tenfold increase in concentration of wealdy adsorbing perchlorate results only in the negligible shift of the potential of viscosity minimum (-4 mV). (C) 2014 Elsevier Ltd. All rights reserved.