This document appears to contain information about solubility equilibria and the solubility product constant (Ksp). It provides examples of solubility equilibria expressions for binary and ternary salts dissolving in water. It also discusses how the value of Ksp relates to the solubility of salts, noting that Ksp values can only be used to directly compare the solubility of salts that contain the same number of ions. The document provides examples of calculating Ksp values from known solubility values and vice versa.

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3. Chapter 16
Solubility and
Complex Ion Equilibria

4. Solubility Equilibria
Ksp

5. Copyright © Cengage Learning. All rights reserved
Some salts are less soluble in water. Much remains solid. The very
low water-soluble fraction of these salts, forms an equilibrium.
 Solubility product (Ksp) – equilibrium constant; has only
one value for a given solid at a given temperature.
AgCl(s) Ag+(aq) + Cl–(aq)
Bi2S3(s) 2Bi3+(aq) + 3S2–(aq)
2 33+ 2
sp = Bi S 
      K
Ksp = [Ag+][Cl-]

6. Section 16.1
Solubility Equilibria and the Solubility Product
 Examples:
MgF2 (s) Mg2+ (aq) + 2F- (aq) Ksp = [Mg2+][F-]2
Ag2CO3 (s) 2Ag+ (aq) + CO3
2- (aq) Ksp = [Ag+]2[CO3
2-]
Ca3(PO4)2 (s) 3Ca2+ (aq) + 2PO4
3- (aq) Ksp = [Ca2+]3[PO4
3-]2

8. Calculation the value of Ksp

9. The solubility of calcium sulfate (CaSO4) is found to be
4.9 ×10-3 M. Calculate the value of Ksp for calcium sulfate.
CaSO4 (s) Ca2+ (aq) + SO4
2- (aq)
CaSO4 (s) Ca2+ (aq) + SO4
2- (aq) Ksp = [Ca2+][SO4
2-]
4.9 ×10-3 4.9 ×10-3
Ksp= (4.9 ×10-3)2= 2.4 ×10-5

10. Section 16.1
Solubility Equilibria and the Solubility Product
Solubility of salts (s)

11. Section 16.1
Solubility Equilibria and the Solubility Product
 For Binary salts: AB(s) A+(aq) + B–(aq)
s s
 For ternary salts: AB2(s) A+(aq) + 2B–(aq)
s 2s
Ksp = s2
Ksp = 4s3

12. 16.6

13. What is the solubility of silver chloride in g/L ?
AgCl (s) Ag+ (aq) + Cl- (aq)
Ksp = [Ag+][Cl-]Initial (M)
Change (M)
Equilibrium (M)
0.00
+s
0.00
+s
s s
Ksp = s2
s = Ksp
s = 1.3 x 10-5
[Ag+] = 1.3 x 10-5 M [Cl-] = 1.3 x 10-5 M
Solubility of AgCl =
1.3 x 10-5 mol AgCl
1 L soln
143.35 g AgCl
1 mol AgCl
x = 1.9 x 10-3 g/L
Ksp = 1.6 x 10-10
AgCl (s) Ag+ (aq) + Cl- (aq)

14. Section 16.1
Solubility Equilibria and the Solubility Product
Copyright © Cengage Learning. All rights reserved 14
In comparing several salts at a given temperature,
does a higher Ksp value always mean a higher
solubility?
No. In order to relate Ksp values to solubility directly, the
salts must contain the same number of ions. For example,
We can compare the solubility of a binary salt with
another binary salt only.
Example: Solubility of AgCl > PbS because
Ksp(Agcl)>Ksp(PbS).
Then: we can not compare the binary salt with ternary
CONCEPT CHECK!

15. Section 16.1
Solubility Equilibria and the Solubility Product
 Other example:
 Arrange the following salts according to solubility.

16. Section 16.1
Solubility Equilibria and the Solubility Product
16
3s s
Ksp= [Ag+]3[PO4
3-]=27S4 S= 1.6×10-5 M
EXERCISE!
Ag3PO4 (s) 3Ag+ (aq) + PO4
3- (aq)
Calculate the solubility of silver phosphate in water.
Ksp = 1.8 × 10–18