The effect of the oxidation state of the metal on the solubility was analyzed using the example of CuCl_x-MCl-H₂O (x = 1, 2; M = Li-Cs, NH₄) ternary systems. The prevalence of acido complex formation is responsible for an essential similarity of the solubility isotherms: the presence of crystallization branches of complex salts and salting-in (or weak salting-out) of copper(I) and (II) chlorides, that increases in the order LiCl < NaCl < KCl < CsCl. The different stability of copper(I) and (II) chloride complexes results in that the chemical individuality of alkali metal cations is differently reflected in the shape of the solubility isotherms: The stronger complex formation in copper(I) systems results in leveling of this effect and the weaker complex formation with copper(II), in its differentiation.