Ksp Calculator

Calculator

Mode

Choose what you want to compute.

Salt label

Used for display and exports.

Stoichiometry (A_aB_b)

a b

Example CaF₂: a=1, b=2.

Ksp

Required for solubility or ions modes.

Molar solubility, s (mol/L)

Required for Ksp-from-solubility mode.

Include common-ion concentrations

Adds A0 and B0 to the equilibrium expression.

Initial [Cation], A0 (mol/L)

Set to 0 for pure water.

Initial [Anion], B0 (mol/L)

Useful for salts in a shared electrolyte.

Tip: Use consistent units (mol/L). Ksp values depend on temperature; keep your Ksp and scenario at the same temperature.

Example data table

Salt	Stoichiometry (a,b)	Typical Ksp	Model note
AgCl	(1,1)	~1.8×10⁻¹⁰	Classic 1:1 salt in pure water.
CaF₂	(1,2)	~1.5×10⁻¹⁰	Higher anion power increases nonlinearity.
Al(OH)₃	(1,3)	Very small	Often influenced by pH and complexation.
PbI₂	(1,2)	Small	Common-ion I⁻ sharply lowers solubility.

Values vary by temperature and reference source.

Formula used

For A_aB_b(s) ⇌ aA⁺ + bB⁻

Ksp = [A]^a[B]^b
Pure water: [A]=a·s, [B]=b·s, so Ksp=(a·s)^a(b·s)^b
Solving for s (pure water): s = (Ksp / (a^ab^b))^1/(a+b)
Common ions: Ksp=(A0+a·s)^a(B0+b·s)^b (solved numerically)

This calculator assumes activities ≈ concentrations. At higher ionic strength, activity coefficients can matter.

How to use this calculator

Pick a mode: solubility, Ksp, or equilibrium ions.
Enter the salt stoichiometry a and b.
Provide Ksp or s, depending on mode.
Optional: enable common ions and enter A0 and B0.
Press Submit to see results below the header.
Use the download buttons to export CSV or PDF.

FAQs

1) What does Ksp represent?

Ksp is the equilibrium constant for a sparingly soluble salt dissolving into ions. Smaller values generally mean lower solubility under similar conditions.

2) Why do I need a and b?

The exponents in the Ksp expression match ion coefficients. A 1:2 salt uses powers 1 and 2, changing both the equation and the solubility curve.

3) What units should I use?

Use mol/L for ion concentrations and molar solubility. Ksp is unitless in strict thermodynamics, but calculations assume consistent concentration units.

4) How does the common-ion effect work here?

Initial ions A0 or B0 increase the ion product. The solver finds the extra dissolution s that brings the ion product back to Ksp.

5) Why can the solver return s = 0?

If A0 and B0 already satisfy or exceed Ksp, dissolving more solid is not favored. The model reports negligible additional dissolution.

6) Does temperature matter?

Yes. Ksp values depend on temperature. Use a Ksp value measured at the same temperature as your solution scenario for reliable results.

7) What about complex ions or pH effects?

This tool uses a basic Ksp model with concentrations. Complexation, hydrolysis, or pH-dependent equilibria can change solubility beyond this calculation.

8) Why do results sometimes look scientific?

Very small or very large values are shown in scientific notation to stay readable and avoid rounding away important magnitude differences.