Thus if Ag⁺ and Cl^- are in balance in pure water, and if more Cl^- is added from another salt, then Ag⁺ and Cl^- will combine and precipitate as solid AgCl until the product of [Ag⁺] and [Cl^-] once again is as low as K_sp for AgCl.

Solubility-constant expressions can be written for all slightly soluble salts. Salts such as NaCI are very soluble, and their K_sp's are effectively infinite, as far as solubility-product calculations are concerned. Soluble and slightly soluble salts resemble strong and weak acids, for although in theory there is no sharp demarcation between the two categories, in practice the division between two kinds of behavior is useful.

Solubility-product constants for various salts are given in the table across. Remember that these come from equilibrium-constant expressions, so if dissociation of a mole of a salt produces n moles of one of the ions, that ion will appear in the K_sp expression as the nth power of the concentration. For example,