A general systematic approach is proposed for the numerical calculation of multi-equilibrium problems. The approach involves several steps: (i) the establishment of balances involving the chemical species in solution (e.g., mass balances, charge balance, and stoichiometric balance for the reaction products), (ii) the selection of the unknowns (the concentration of selected chemical species at equilibrium), (iii) the estimation of the concentration of the other species based on the selected species and the equilibrium expressions, and (iv) the minimization of the sum of the squared balances (search of the optimal combination of the unknowns). The application of the systematic approach to cases of diverse complexity, involving acid−base reactions, redox reactions, and the formation of complexes and solids in aqueous solution, using the Solver option of the Excel spreadsheet is shown. The approach is useful to solve problems of high complexity. It might be useful to undergraduate students in the field of solution equilibria, and they would also gain experience with a method for solving simultaneous equations.

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