The oxidation of Ag in the presence of 4,4’-bipyridyl (Bpy) has been studied by combined cyclic voltammetric and mass measurements (derived from the electrochemical quartz crystal microbalance). A Ag(I)-Bpy complex is formed at the electrode surface, but observed mass changes are found to result from the superposition of a mass loss (from release of Ag+) and a mass gain (from complex precipitation). Altering the conditions of the experiment (scan rate, upper potential Limit and bipyridyl concentration) can switch the balance between the two processes and lead to a net mass loss or a net mass gain; at slow scan rates at a bulk concentration of 0.25 mM bipyridyl, the balance between the processes switches twice, even in the narrow potential range before complex reduction. The principal cause of these changes is the slow accumulation of Ag+ in the diffusion layer as not all the Ag+ released is complexed. At higher concentrations of bipyridyl (2 mM) mass changes due to complex formation are dominant until the potential is extended such that the surface concentration of bipyridyl is significantly depleted and electrode corrosion makes the principal contribution to the mass change.