This paper reports the results of impedance measurements of emeraldine form of polyaniline subjected to different doping procedures. It is shown that a suitable impedance function to describe the electrical properties of the polymer is the complex electric modulus. It allows us to distinguish different modes of the electrical relaxation. Characteristic relaxation time depends on the doping level, temperature and concentration of water absorbed in the polymer matrix. It is shown that each additional molecule of H2O absorbed by one polymeric unit (consisting of four aniline cores) results in a ten-fold decrease of the relaxation time. Useful information about electrical properties of conducting polymers might also be obtained from the analysis of frequency dependencies of electric loss factor. Combining the impedance measurements with those of thermogravimetry and calorimetry we have shown the identity of acid doping mechanisms with that provoked by water molecules or similar solvents. A generalized scheme of interaction between the polymer and solvent through the formation of H-bonds is proposed H-bonding at imine centres results in dissociation of the solvent molecule and protonation of the polymer. Electric charge is then delocalized over the polymer chain thus causing its linearization, conjugation of aniline cores and increase of the electrical conductivity of the polymer.