Show that, if the ionic strength of a solution of the sparingly soluble salt MX and the

Question:

Show that, if the ionic strength of a solution of the sparingly soluble salt MX and the freely soluble salt NX is dominated by the concentration C of the latter, and if it is valid to use the Debye--Huckel limiting law, the solubility S' in the mixed solution is given by S = Kse4.606Ac/2 when K, is small (in a sense to be specified).