This chapter describes background information associated with a systematic approach to acid-base equilibria. Several types of equations, including the autoprotolysis constant for water, mass-balance equations, and concentration-fraction equations are discussed in this chapter. The autoprotolysis constant for water is used to quantify the relationship between the hydrogen ion and hydroxide ion concentrations. Mass-balance equations are used to establish relationships among initial concentrations of different forms of weak acids and the total concentrations of all forms of the acids. Numbers, i, of protons lost in successive deprotonation steps of weak acids are used to identify quantities such as concentration fractions and diluted concentrations of the different forms of weak acids. Equations for concentration fractions are used with total concentrations of all forms of each weak acid to calculate equilibrium concentrations of the different forms of the acid. Cumulative deprotonation constants representing products of all constants up to and including each step in stepwise deprotonation reactions are used to simplify equations for concentration fractions. The resulting equations are used to develop a spreadsheet program to calculate concentration fractions. The program is incorporated into a template to calculate concentration fractions for acids with up to six acidic hydrogens each. The template includes a feature to prepare plots of concentration fractions vs. pH called distribution plots. Distribution plots are used help us visualize how fractions of weak acids in different forms depend on pH.