Solubility Product (Ksp) Calculator
Calculate the solubility product constant (Ksp) from molar solubility and salt stoichiometry.
Scientific notation is accepted (e.g. 1e-3 means 1 × 10⁻³).
Solubility Product (Ksp)
Calculation Steps
What Is the Solubility Product?
The solubility product constant (Ksp) is the equilibrium constant for the dissolution of a sparingly soluble ionic compound in water. For a saturated solution, it equals the product of the molar concentrations of the dissolved ions, each raised to the power of its stoichiometric coefficient. A larger Ksp indicates a more soluble salt. Given the molar solubility s (mol/L) and the salt's dissolution stoichiometry, Ksp can be computed directly.
Ksp Expressions by Salt Type
The relationship between Ksp and molar solubility s depends on how many ions the salt produces when it dissolves:
AB (e.g. AgCl): Ksp = s²
AB₂ (e.g. CaF₂): Ksp = 4s³
A₂B (e.g. Ag₂CrO₄): Ksp = 4s³
AB₃ (e.g. Fe(OH)₃): Ksp = 27s⁴
A₂B₃ (e.g. Ca₃(PO₄)₂): Ksp = 108s⁵
- • s = molar solubility of the salt (mol/L)
- • Ksp = solubility product constant (dimensionless)
Common Salt Types
| Type | Example | Ksp Expression |
|---|---|---|
| AB | AgCl, BaSO₄ | s² |
| AB₂ | CaF₂, PbCl₂ | 4s³ |
| A₂B | Ag₂CrO₄ | 4s³ |
| AB₃ | Fe(OH)₃ | 27s⁴ |
| A₂B₃ | Ca₃(PO₄)₂ | 108s⁵ |
Note: This calculator assumes ideal behavior in dilute aqueous solution and that the salt dissolves into its stoichiometric ions without complexation, ion pairing, or the common-ion effect. Reported Ksp values are temperature dependent (usually quoted at 25 °C). For precise analytical work, account for activity coefficients and ionic strength.