Diffusion coefficients of an aqueous system containing ferric sulfate 0.05 mol . dm(-3) and lactose at different concentrations at 25 degrees C have been measured, using a conductimetric cell and an automatic apparatus to follow diffusion. The cell uses an open-ended capillary method and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times. These data permit us to have a better understanding of the transport behaviour of ferric sulfate in different media. These studies have been complemented by molecular mechanics and ab initio calculations. (C) 2013 Elsevier Ltd. All rights reserved.