Loading....
Coupon Accepted Successfully!

 

Solubility Product


There are many salts that are sparingly soluble in water. Examples are AgCl, BaSO4, CaF2, Ca3(PO4)2 and PbI2. When such a salt is placed in water, a small quantity passes into water as ions. A dynamic equilibrium between the solid and its characteristics ions exists in the solution. Taking the example of AgCl, we have
AgCl(s) Ag+(aq) + Cl-(aq)

At the equilibrium position, the rate of dissolution of ions from the solid is equal to the rate of precipitation of ions from the saturated solution. As usual, the equilibrium can be characterized by equilibrium constant. In the present case, we have


Since the concentration of a pure solid has a constant value, the concentration of solid AgCl may be combined with Keq to give a new constant, called the solubility product.
Ksp = Keq[AgCl(s)] = [Ag+(aq)][Cl-(aq)]

Thus, the solubility product is equal to the product of the ionic concentrations present in a saturated solution. When the salt dissolves to give an unequal number of positive and negative ions, each concentration term is raised to a power equal to the coefficient of the ion appearing in the equation.
   

    Expressions of solubility product for a few sparingly soluble salts

Salt

Reaction

Solubility product expression

CaF2

CaF2 Ca2+ + 2F-

Ksp(CaF2) = [Ca2+] [F-]2

PbI2

PbI2 Pb2+ + 2I-

Ksp(PbI2) = [Pb2+] [I-]2

Hg2Cl2

Al(OH)3

Al(OH) Al3++3OH-

Ksp(Al(OH)3)=[Al3+][OH-]3

Ag3(Po4)

Ag3(PO4) 3Ag++

Ca3(PO4)2

Ca3(PO4)23Ca2++


Since the solubility of a salt varies with temperature, the numerical value of Ksp for a salt changes with temperature. These values are usually recorded at 25 ° C.
 

Values of solubility products for a few sparingly soluble salts

Salt

Ksp

Salt

Ksp

AgCl

1.7 × 10-10 (mol dm-3)2

PbCl2

1.6 × 10-5(mol dm-3)3

AgBr

5.0 × 10-13 (mol dm-3)2

Hg2Cl2

1.1 × 10-18(mol dm-3)3

AgI

8.5 × 10-17 (mol dm-3)2

Mg(OH)2

8.9 × 10-13(mol dm-3)3

BaCO3

1.6 × 10-8 (mol dm-3)2

PbI2

8.3 × 10-9(mol dm-3)3

BaSO4

1.5 × 10-9 (mol dm-3)2

Ca(OH)2

1.3 × 10-6(mol dm-3)3

BaCrO4

8.5 × 10-11 (mol dm-3)2

Al(OH)3

5.0 × 10-33(mol dm-3)4

HgS

3.0 × 10-53 (mol dm-3)2

CdS

1.0 × 10-28(mol dm-3)2

ZnS

2.5 × 10-22(mol dm-3)2

CoS

7 × 10-23(mol dm-3)2





Test Your Skills Now!
Take a Quiz now
Reviewer Name