Solubility Product (Ksp) Calculator
Calculate the solubility product constant (Ksp) from molar solubility, or find how much of a salt dissolves given its Ksp. Supports common salt types (AB, A2B, AB2, A3B) and the common ion effect, which reduces solubility when a shared ion is already present in solution.
The solubility product constant (Ksp) describes how much of a sparingly soluble salt dissolves in water. It is the equilibrium constant for the dissolution reaction.
What Is Ksp?
For a generic salt AxBy that dissolves as:
AxBy(s) -> xA(aq) + yB(aq)
The solubility product is:
Ksp = [A]^x * [B]^y
Common Salt Types
| Type | Example | Ksp Expression |
|---|---|---|
| AB | AgCl | Ksp = s^2 |
| A2B | Ag2CrO4 | Ksp = (2s)^2(s) = 4s^3 |
| AB2 | CaF2 | Ksp = (s)(2s)^2 = 4s^3 |
| A3B | Ag3PO4 | Ksp = (3s)^3(s) = 27s^4 |
Where s = molar solubility.
Worked Example: AgCl
AgCl has Ksp = 1.77 x 10^-10.
s = sqrt(Ksp) = sqrt(1.77 x 10^-10) = 1.33 x 10^-5 mol/L
That means only 0.00133% of a mole of AgCl dissolves per liter of water.
The Common Ion Effect
If you dissolve AgCl in a 0.10 M NaCl solution, the Cl- already present pushes the equilibrium back:
Ksp = [Ag+][Cl-] = s(0.10 + s) ≈ s(0.10)
s = 1.77 x 10^-10 / 0.10 = 1.77 x 10^-9 mol/L
The solubility drops by nearly 10,000x compared to pure water. This is the common ion effect in action.