Electrochemical dissolution of iron(III) and chromium(III) oxides can be described as an irreversible reaction of homogeneous, continuous sets of particles or as a mixture of such sets. Each set can be characterized by the rate constant at reference potential, charge-transfer coefficient and heterogeneity factory γ within a certain potential range in which not mass transport but electron transfer controls the overall reaction rate. This condition is easy to maintain in the case of chronoamperometry but not in the case of linear sweep voltammetry at a scan rate of 1 mV s⁻¹ or more. However, the commonly used relationship between the potential of a voltammetric peak and the kinetic characteristics of the charge-transfer is valid. The commonly used exponential shape of chronoamperometric curve is a special case for certain size distributions of particles. The influence of the heterogeneity factor γ on the shape of voltammetric peak is discussed. According to the results obtained, abrasive stripping voltammetry is a more effective tool for studying solid compounds than the carbon paste method, because of negligible disturbance from dissolved species and a correspondingly simpler voltammetric curve, as demonstrated here in the case of CuFe₂O₄.