Chapter 16

Solubility and Complex Ion Equilibria

Section 16.1

Solubility Equilibria and the Solubility Product

Solubility Equilibria   Solubility product (K sp ) – equilibrium constant; has only one value for a given solid at a given temperature.

Solubility – an equilibrium position.

Bi 2 S 3 (s) 2Bi 3+ (aq) + 3S 2– (aq)

K

sp = Bi 3+ 2   S 2  3 Copyright © Cengage Learning. All rights reserved 2

Section 16.1

Solubility Equilibria and the Solubility Product

CONCEPT CHECK!

In comparing several salts at a given temperature, does a higher K solubility ? sp value always mean a higher Explain. If yes, explain and verify. If no, provide a counter-example.

Copyright © Cengage Learning. All rights reserved 3

Section 16.1

Solubility Equilibria and the Solubility Product

EXERCISE!

Calculate the solubility of silver chloride

K

sp = 1.6 × 10 –10 in water. Calculate the solubility of silver phosphate

K

sp = 1.8 × 10 –18 in water. Copyright © Cengage Learning. All rights reserved 4

Section 16.1

Solubility Equilibria and the Solubility Product

EXERCISE!

Calculate the solubility of AgCl in:

K

sp = 1.6 × 10 –10 a) 100.0 mL of 4.00 x 10 -3

M

calcium chloride .

b) 100.0 mL of 4.00 x 10 -3

M

calcium nitrate .

Copyright © Cengage Learning. All rights reserved 5

Section 16.2

Precipitation and Qualitative Analysis

Precipitation (Mixing Two Solutions of Ions)   Q > K sp ; precipitation occurs and will continue until the concentrations are reduced to the point that they satisfy K sp .

Q < K sp ; no precipitation occurs.

Copyright © Cengage Learning. All rights reserved 6

Section 16.2

Precipitation and Qualitative Analysis

Selective Precipitation (Mixtures of Metal Ions)   Use a reagent whose anion forms a precipitate with only one or a few of the metal ions in the mixture.

Example:  Solution contains Ba 2+ and Ag + ions.

 Adding NaCl will form a precipitate with Ag while still leaving Ba 2+ in solution.

+ (AgCl), Copyright © Cengage Learning. All rights reserved 7

Section 16.2

Precipitation and Qualitative Analysis

Separation of Cu 2+ and Hg 2+ from Ni 2+ and Mn 2+ using H 2 S   At a low pH, [S 2– ] is relatively low and only the very insoluble HgS and CuS precipitate.

When OH – is added to lower [H + ], the value of [S 2– ] increases, and MnS and NiS precipitate.

Copyright © Cengage Learning. All rights reserved 8