Applications of Environmental Aquatic Chemistry, 3rd Edition

553Appendix B

Example 5: Determine the pH Dependence of the Solubility

of Salts that Change the Concentrations of Hydroxyl

(OH

−

) or Hydrogen (H

+

) Ions when Dissolved

When dissolving a salt into water changes the hydroxyl or hydrogen ion

concentrations,* the solubility of that salt will be pH dependent.

A. Show that the solubility of the salt Mg(OH)

2

is pH dependent.

1. The dissolution reactions from Equations B.4 and B.5 are repeated below:

AgNO (s)Ag(aq)NO(aq)

3

HO

3

2

→ +

+−

NaCl(s)NaaqClaq

HO

+

2

→ +

−

()

()

Because both salts are highly soluble, after the salts dissolve and before

any further reaction, the solution would contain 20 mg/L each ...