means the charge-equivalent concentration of single-charge ions. For example, 1 mole of in solution represents 1 molar equivalent, while 1 mole of is 2 molar equivalents because twice as many H⁺ ions would be necessary to balance the charge. The total charge of a solution always equals zero. This leads to a parallel definition of alkalinity that is based upon the charge balance of ions in a solution.

Certain ions, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-,