ABSTRACT
Solving a chemical problem requires knowledge of the equations that govern the problem. For chemical speciation problems, equilibrium constant expressions are among the equations that are needed. Other important equations include the electroneutrality equation (ENE), mass balance equations (MBEs), and the proton balance equation, if one can be written for the system. The ENE is the mathematical statement that an aqueous solution must be electrically neutral. The ENE is also known as the charge balance equation. Since the ENE involves multiple species in a solution, it is very useful in solving problems. It is always possible to write an ENE for an aqueous solution: one just has to know which ions are present in solution, and it can be written. And, if one knows how the solution came to be, governing MBE(s) for the solution can also always be written.
