Mass transfer is an integral part of numerous processes in chemical engineering. Depending on the hydrodynamic conditions within the system, that transfer can occur through molecular diffusion or convection mechanism. In this thesis, mass transfer rate was analysed, focusing exclusively on molecular diffusion mechanism. The effect of concentration of sodium chloride solution on the diffusion coefficient was examined. Diffusion coefficients, whose numerical values give a direct insight in the mass transfer rate, in this work were determined experimentally and using Wilke-Chang’s equation. The results of the experimental measurements, as opposed to the theoretical values obtained, indicate that, with increasing NaCl solution concentration, the value of the diffusion coefficient increases as well. Experimentally and theoretically determined numerical values of the diffusion coefficient do not display an adequate congruence. The possible reasons for said deviation can be of experimental nature, but also caused by the utilization of an unsuitable equation, in the case of solutions which are strong electrolytes. The main causes of experimental errors could be: inadequate mixing of the solution whose electrical conductivity is being measured, variation in temperature during the experiment, the occurrence of air bubbles within the diffusion cell, conductometric measurements which were taken in only one position in the mixing vessel and eventual mistakes during the preparation of the solutions. In future work, it would be useful to minimize the effect of the said experimental mistakes, and to utilize a more suitable equation for the calculation of the theoretical diffusion coefficient, which takes into consideration the nature of the analysed solution in a more strict manner.