An analysis process involves the separation of the analyte from interferences. The precipitation can be used as a separation step when analyte is precipitated as an insoluble compound in a gravimetric analysis procedure. It must be determined the appropriate conditions such as the interval pH of solution, the volume and the interval of concentration of precipitating reagent for a successful quantitative precipitation procedure. In this context, the aim of this study is to model for the teaching of quantitative precipitation in analytical chemistry teaching how the stoichiometric calculations can be done to determine hypothetically the appropriate conditions for the quantitative precipitation. Three problems and their solutions are given for this aim. The appropriate conditions for the quantitative precipitation are also valid for the separability of analyte such as Fe3+ from interference such as Mn2+ by the precipitation procedure.