🧂 Ksp & Molar Solubility Calculator
Enter a salt's Ksp and ion subscripts to get its molar solubility (or go the other way) — including the common-ion effect.
Molar solubility (pure water)
1.342e-5 M
With common ion
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For a salt AₐBᵦ ⇌ a·Aⁿ⁺ + b·Bᵐ⁻, Ksp = (a·s)ᵃ·(b·s)ᵇ = aᵃ·bᵇ·s^(a+b), so s = (Ksp ÷ (aᵃ·bᵇ))^(1/(a+b)). A common ion (already in solution) shifts the equilibrium left and suppresses solubility — the tool solves that case numerically. Ksp values vary with temperature and source; enter the one from your data. 🔒 In your browser.
How the ksp & molar solubility calculator works
For a sparingly soluble salt AₐBᵦ dissolving as a·Aⁿ⁺ + b·Bᵐ⁻, the solubility product is Ksp = (a·s)ᵃ·(b·s)ᵇ = aᵃ·bᵇ·s^(a+b), where s is the molar solubility. The tool rearranges this to s = (Ksp ÷ (aᵃ·bᵇ))^(1/(a+b)), converts either direction, and — if you supply a common-ion concentration — solves the suppressed solubility numerically.
Watch the stoichiometry: the exponents come from the ion subscripts, which is exactly where the arithmetic trips people up (Ag₂CrO₄ is 2:1, so Ksp = 4s³, not s²). A common ion already in solution shifts the dissolution equilibrium left and sharply lowers solubility. Ksp values change with temperature and vary between sources, so use the value from your own data.
Frequently asked questions
How do I calculate molar solubility from Ksp?
Write the dissolution equation, express Ksp in terms of s using the ion coefficients, and solve. For AgCl (1:1), Ksp = s², so s = √Ksp = √(1.8×10⁻¹⁰) ≈ 1.3×10⁻⁵ M. The tool handles any stoichiometry.
What is the solubility product Ksp?
The equilibrium constant for a solid dissolving into its ions: Ksp = product of the ion concentrations, each raised to its coefficient. A smaller Ksp means a less soluble salt.
How does the common-ion effect work?
Adding an ion the salt already contains (e.g. dissolving AgCl in NaCl solution) pushes the dissolution equilibrium backward, so much less of the salt dissolves. The tool computes the reduced solubility when you enter the common-ion concentration.
Why is Ag₂CrO₄ not just √Ksp?
Because its stoichiometry is 2:1 — it releases 2 Ag⁺ and 1 CrO₄²⁻, so Ksp = (2s)²(s) = 4s³. You must build the Ksp expression from the coefficients, which is why the subscripts matter here.
Does temperature change Ksp?
Yes — Ksp is temperature-dependent (usually rising with temperature for most salts). Published values are typically at 25 °C; use the value that matches your conditions.