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808 Chapter 15 | Equilibria of Other Reaction Classes
(b)
(c)
(d)
(e)
Check Your Learning
Write the ionic equation for the dissolution and the solubility product for each of the following slightly soluble compounds:
(a) BaSO4
(b) Ag2SO4 (c) Al(OH)3 (d) Pb(OH)Cl
Answer:
(a)
(b) (c) (d)
Now we will extend the discussion of Ksp and show how the solubility product is determined from the solubility of its ions, as well as how Ksp can be used to determine the molar solubility of a substance.
Ksp and Solubility
The Ksp of a slightly soluble ionic compound may be simply related to its measured solubility provided the dissolution
process involves only dissociation and solvation, for example:
For cases such as these, one may derive Ksp values from provided solubilities, or vice-versa. Calculations of this sort are most conveniently performed using a compound’s molar solubility, measured as moles of dissolved solute per liter of saturated solution.
Example 15.2
Calculation of Ksp from Equilibrium Concentrations
We began the chapter with an informal discussion of how the mineral fluorite (Figure 15.1) is formed.
Fluorite, CaF2, is a slightly soluble solid that dissolves according to the equation:
The concentration of Ca2+ in a saturated solution of CaF2 is 2.15 10–4 M; therefore, that of F– is 4.30
10–4 M, that is, twice the concentration of Ca2+. What is the solubility product of fluorite? Solution
First, write out the Ksp expression, then substitute in concentrations and solve for Ksp:
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