24
Solubility Product and Precipitation
In Chapter 23, we discuss applications of equilibrium relations to the pH of
aqueous solutions. Another important application of these principles is to precipitation reactions.
We tend to think of the precipitates we separate in chemical analysis as
insoluble. Actually, any precipitate is somewhat soluble. When we have a
precipitate of AgCl, for example, in contact with supernatant liquid, the liquid
is saturated with the ions of the precipitate, Ag
+ and Cl~. The equation is
AgCl< s) ?± Ag+ + ClThe symbol (s) designates a solid. At the surface of the precipitate, Ag
+ and
Cl~ ions are constantly going into solution and redepositing from the solution.
Because this is an equilibrium process, we can apply the mathematical relation
[AgCU
e
The concentration of solid AgCl crystals is constant and invariable, so we
may simplify the equation by combining the two constants:
[Ag
+ ][Cl-] = K e x [AgCU = *s P
Solubility Product and Precipitation
In Chapter 23, we discuss applications of equilibrium relations to the pH of
aqueous solutions. Another important application of these principles is to precipitation reactions.
We tend to think of the precipitates we separate in chemical analysis as
insoluble. Actually, any precipitate is somewhat soluble. When we have a
precipitate of AgCl, for example, in contact with supernatant liquid, the liquid
is saturated with the ions of the precipitate, Ag
+ and Cl~. The equation is
AgCl< s) ?± Ag+ + ClThe symbol (s) designates a solid. At the surface of the precipitate, Ag
+ and
Cl~ ions are constantly going into solution and redepositing from the solution.
Because this is an equilibrium process, we can apply the mathematical relation
[AgCU
e
The concentration of solid AgCl crystals is constant and invariable, so we
may simplify the equation by combining the two constants:
[Ag
+ ][Cl-] = K e x [AgCU = *s P