What is a solubility product?

1 Answer
Jul 11, 2015

Answer:

The solubility product, #K_{sp}#, is simply another equilibrium expression, and quantitatively defines the solubility of a salt in water (the most usual solvent).

Explanation:

Consider the solubility of the "insoluble" salt, silver chloride, AgCl, in water. We could represent its dissolution as:

#AgCl(s) rarr Ag^+ + Cl^-#

#K_(sp) = [Ag^+][Cl^-] = 1.8 xx10^-10# at 298 K (solubility products are extensively and exhaustively tabulated for a host of sparingly soluble salts. Only the products appear in the equilibrium expression because the concentration of a solid material, here #AgCl#, is undefined.

So to determine the solubility of AgCl in water, and knowing that #[Ag^+] = [Cl^-]#, we simply have to solve an equation in #x^2#, where #x# = solubility. It follows that if the concentration of chloride ion is artificially increased (say by adding #NaCl#), #[Ag^+]#, remaining in solution, might be reduced even further (this is called "salting out").

Would #K_(sp)# be expected to increase with increasing temperature?