Solubility Product Principle
Definition and meaning of Solubility Product Principle in chemistry.
The solubility product principle states that for a sparingly soluble salt in equilibrium with its dissolved ions, the product of the molar concentrations of each ion, each raised to the power of its stoichiometric coefficient, is constant at a given temperature. This constant is called the solubility product constant, or Ksp.
In more detail
At equilibrium, a saturated solution of a sparingly soluble salt maintains a constant product of ion concentrations. For example, when silver chloride dissolves in water, the product [Ag+][Cl-] always equals Ksp (1.8 × 10-10 at 25°C). The principle allows chemists to predict whether a precipitate will form when two solutions are mixed, and to calculate the solubility of sparingly soluble salts under various conditions, including when a common ion is already present.
Key facts
| Formula | Ksp = [A]a[B]b... (at constant temperature) |
|---|---|
| Example compound | Silver chloride (AgCl) |
| Application | Predicting precipitation and calculating solubility |
| Field | Physical Chemistry |
For silver chloride (AgCl) with Ksp = 1.8 × 10-10 at 25°C, the dissolution equilibrium is: AgCl(s) ⇌ Ag+(aq) + Cl-(aq), and the solubility product expression is Ksp = [Ag+][Cl-] = 1.8 × 10-10.
Frequently asked questions
What does Ksp tell you about a salt's solubility?
A smaller Ksp indicates lower solubility, while a larger Ksp indicates higher solubility. The exact molar solubility can be calculated from Ksp.
How does the common ion effect relate to the solubility product principle?
When a common ion is added to a saturated solution, Ksp remains constant; therefore, the other ion's concentration must decrease to maintain the product, reducing the salt's solubility.