Solubility product calculator
Choose the type of salt by its formula, then enter Ksp as a number times a power of ten to get how much of the salt dissolves in pure water, or enter a solubility to get Ksp. Give the molar mass to work in grams per litre. The ion concentrations and pKsp are shown too.
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How to use it
- Choose what to find: solubility from Ksp, or Ksp from a measured solubility.
- Pick the salt type, AB, AB₂, A₂B and so on, by the numbers of cations and anions in the formula.
- Enter Ksp as mantissa and power of ten, or the solubility. For g/L, give the molar mass.
- Ksp from solubility: Ksp = (x·s)ˣ × (y·s)ʸ = xˣ·yʸ·s^(x+y).
- Solubility from Ksp: s = (Ksp ÷ (xˣ·yʸ))^(1 ÷ (x + y)).
- In g/L: s × M. pKsp = −log₁₀ Ksp.
Worked example
Silver chloride, AB, with Ksp = 1.8 × 10⁻¹⁰: s = √(1.8 × 10⁻¹⁰) = 0.00001342 mol/L (1.342 × 10⁻⁵), and pKsp = 9.745. With M = 143.32 g/mol that is 0.001923 g/L, about 1.9 mg per litre.
Calcium fluoride, AB₂, with Ksp = 3.9 × 10⁻¹¹: 4s³ = 3.9 × 10⁻¹¹, so s = ∛(9.75 × 10⁻¹²) = 0.00021363 mol/L and [F⁻] = 0.00042727 mol/L.
Tips
- Ksp values in tables differ with source and temperature; most are given at 25 °C.
- Mind the formula. Fe(OH)₃ is AB₃ (one Fe³⁺, three OH⁻), Ca₃(PO₄)₂ is A₃B₂.
- To check precipitation, compare the ion product Q with Ksp: if Q > Ksp, a precipitate forms.
Frequently asked questions
How do I get molar solubility from Ksp?
Write the dissolution AₓBᵧ ⇌ xA + yB. If s mol/L dissolve, [A] = x·s and [B] = y·s, so Ksp = xˣ·yʸ·s^(x+y). Solve for s. For AgCl (AB) that is simply s = √Ksp; for CaF₂ (AB₂), Ksp = 4s³.
How do I enter a Ksp like 1.8 × 10⁻¹⁰?
Type 1.8 in the first field and −10 in the second. Small results are shown with up to eight decimals, such as 0.00001342 mol/L, and values below 10⁻⁸ in scientific notation, such as 3.2E-11, which means 3.2 × 10⁻¹¹.
Can I compare solubilities by Ksp alone?
Only for salts of the same type. AgCl has a larger Ksp than Ag₂CrO₄, yet Ag₂CrO₄ is more soluble in mol/L, because the formulas differ. Compare the molar solubilities instead.
What does this calculator not include?
It assumes pure water, ideal behaviour and no side reactions. A common ion lowers solubility, and ions that react with acid or form complexes can raise it.