PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 393

11.7 Solubility of sparingly soluble salts

If the concentration of a saturated solution of the salt Bν+Aν− is lower than about 0.01
mol dm−^3 , we speak about a sparingly soluble salt. An equilibrium between the undis-
solved and dissolved salt is established in the system. The dissolved salt dissociates into ions
completely. Overall we may write

Bν+Aν−(s) =ν+Bz

+

+ν−Az

−

. (11.106)

The equilibrium constant of this reaction is called thesolubility productKs. We have

Ks=

aν

+

Bz+a

ν−

Az−

aBν+Aν−

=cν

+

Bz+c

ν−

Az−γ

ν

±(c

st)−ν, (11.107)

whereν=ν++ν−.

Example

The solubility product of silver chromate at a temperature of 298 K and the standard pressure is

Ks= 9× 10 −^12. Calculate the solubility of silver chromate

a) given thatγ±= 1,

b) given that the Debye-H ̈uckel relation with the constantA= 1.176 applies.