Cyclic voltammetry and impedance have been employed for the quantitative study of 2-methyl-2-butanol (tert-PenOH) adsorption kinetics at the bismuth single crystal plane / aq. Na,SO, solution interface. Analysis of impedance data demonstrates that the adsorption process of tert-PenOH is mainly limited by the rate of diffusion of the organic compound to the electrode surface. However, at small frequencies and higher tert-PenOH concentrations, noticeable deviations of the system from a purely diffusion-limited mechanism have been established. These deviations are mainly caused by the two-dimensional association of tert-PenOH molecules in the adsorption layer. Non-linear regression analysis has been used for the simulation of the experimental complex plane (Z", Z') plots. The Frumkin-Melik-Gaikazyan equivalent circuit (where C-true is a double layer capacitance and AC is an adsorption capacitance, Z(W)-Warburg-like diffusion impedance and R-cl is the electrolyte resistance at ac frequency --> infinity) and other equivalent circuit elements have been used for the simulation of experimental impedance data.