http://www.ck12.org Chapter 19. Equilibrium
19.3 Solubility Equilibrium
Lesson Objectives
- Write solubility product constant expressions for nearly insoluble ionic compounds.
- Calculate the value of Ks pfor a compound from its solubility and determine the solubility of a compound with
a known Ks p. - Use the Ks pof a compound to predict whether a precipitate will form when two solutions are mixed together.
- Describe the common ion effect and its relationship to solubility.
Lesson Vocabulary
- common ion
- common ion effect
- molar solubility
- solubility product constant
Check Your Understanding
Recalling Prior Knowledge
- What is a saturated solution?
- What is the equilibrium that occurs in a saturated solution?
A saturated aqueous solution is one in which the maximum amount of a solute has been dissolved in a given amount
of water. A saturated solution may also have undissolved solute present, in which case an equilibrium exists between
the dissolved and undissolved solute. In this lesson, you will learn about that equilibrium and how to calculate and
use the solubility product constant.
The Solubility Product Constant
Ionic compounds have widely differing solubilities. Sodium chloride has a solubility of about 360 g per liter of
water at 25°C. Salts of alkali metals tend to be quite soluble. On the other end of the spectrum, the solubility of zinc
hydroxide is only 4.2× 10 −^4 g/L of water at the same temperature. Many ionic compounds containing hydroxide
are relatively insoluble. The chapterSolutions, summarized a set of rules for predicting the relative solubilities of
various ionic compounds in water.
Most ionic compounds that are considered to be insoluble will still dissolve, to a small extent, in water. These
“mostly insoluble” compounds are still considered to be strong electrolytes because, essentially, any portion of the