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Equilibrium · Solubility

Molar Solubility & Ksp Calculator

Convert between molar solubility and Ksp for a binary ionic solid, including stoichiometric ion powers and optional common-ion concentrations.

Formula shown Runs locally Reviewed Aug 11, 2026
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Equation guide

Saturated dissolution of a binary ionic solid in an ideal dilute solution

Dissolution

AₘBₙ(s) ⇌ mA + nB

Solubility product

Ksp = [A]m[B]n

Ion concentrations

[A] = [A]₀ + ms[B] = [B]₀ + ns
Solubility equilibrium

Connect molar solubility and Ksp

CaF2(s)⇌1 Ca²⁺+2 F⁻
Optional common ions already in solution

Enter zero for an ion absent before dissolution. Scientific notation is accepted; each mantissa may contain at most three decimal places. Displayed results use at most three decimal places.

Ksp

Choose the dissolution stoichiometry and enter Ksp or molar solubility.

Using the model

Symbols, assumptions and limitations

Interpretation notes

The model assumes ideal dilute-solution behavior and complete dissociation of the amount that dissolves. Pure solid is omitted from Ksp. Added common-ion concentrations are treated as fixed initial concentrations; activities, complex formation, acid–base reactions, and competing equilibria are excluded. Tabulated Ksp values depend on temperature and may vary by source.

Worked examples

See the method in practice

01

Silver chloride

For AgCl(s) ⇌ Ag⁺ + Cl⁻ in pure water, Ksp = s² because both equilibrium ion concentrations equal the molar solubility s.

02

Calcium fluoride

For CaF₂(s) ⇌ Ca²⁺ + 2F⁻, Ksp = s(2s)² = 4s³ in pure water. Added fluoride lowers the calculated solubility.

Questions

Frequently asked

Why is molar solubility not always the square root of Ksp?

The ion concentrations depend on dissolution coefficients. Only a 1:1 solid in pure water gives Ksp = s².

What is the common-ion effect?

An ion already present shifts dissolution equilibrium toward the solid, usually reducing molar solubility.

Can I use Ksp to predict precipitation directly?

Compare the ion product Qsp with Ksp: Qsp greater than Ksp indicates supersaturation and possible precipitation. This calculator focuses on saturated dissolution states.

Sources & review

Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.

OpenStax Chemistry — Precipitation and Dissolution

Written by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology