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Ksp and Solubility Calculator
In short: Ksp calculator: convert between Ksp and molar solubility in mol/L or g/L, find solubility with a common ion (solved exactly), and check whether a precipitate forms when two solutions are mixed. It is free, works in your web browser and needs no download.
Pick a salt from the list or enter any MₓAᵧ with its Ksp. Get the molar solubility and g/L, or go from a measured solubility to Ksp. The common-ion mode solves the full equation numerically rather than relying on the shortcut. The precipitation mode compares Q with Ksp after mixing.
Molar solubility s from Ksp = xxyysx+y, in pure water.
Concentration of an ion already in the solution (for example 0.10 M NaCl gives 0.10 M Cl⁻). Fill in one or both.
Enter the ion concentration in each solution before mixing (0.10 M CaCl₂ gives 0.10 M Ca²⁺ but 0.20 M Cl⁻).
Ksp and molar solubility formulas
MₓAᵧ(s) ⇌ x Mʸ⁺(aq) + y Aˣ⁻(aq) Ksp = [M]ˣ[A]ʸ = (xs)ˣ(ys)ʸ = xˣyʸ s^(x+y)
| Salt type | Example | Ksp in terms of s | Solubility s |
|---|---|---|---|
| MA (1:1) | AgCl, BaSO₄ | s² | √Ksp |
| MA₂ or M₂A | CaF₂, Ag₂CrO₄ | 4s³ | (Ksp/4)^(1/3) |
| MA₃ or M₃A | Fe(OH)₃, Ag₃PO₄ | 27s⁴ | (Ksp/27)^(1/4) |
| M₃A₂ or M₂A₃ | Ca₃(PO₄)₂ | 108s⁵ | (Ksp/108)^(1/5) |
Common-ion effect
If the solution already contains c of one ion, solve (xs + cM)ˣ(ys + cA)ʸ = Ksp. The usual shortcut drops s next to c. That works only when s is much smaller than c. This calculator solves the full equation numerically and shows how far off the shortcut is.
Will a precipitate form?
After mixing, find each ion's new concentration (moles ÷ total volume) and calculate the ion product Q = [M]ˣ[A]ʸ. If Q is greater than Ksp, a precipitate forms. If Q is less than or equal to Ksp, it does not.
Ksp values of common salts (25 °C)
| Salt | Ksp | Ksp = | s (mol/L) | s (g/L) | M (g/mol) |
|---|---|---|---|---|---|
| AgCl | 1.8 × 10⁻¹⁰ | s² | 1.3 × 10⁻⁵ | 1.9 × 10⁻³ | 143.32 |
| AgBr | 5.0 × 10⁻¹³ | s² | 7.1 × 10⁻⁷ | 1.3 × 10⁻⁴ | 187.77 |
| AgI | 8.3 × 10⁻¹⁷ | s² | 9.1 × 10⁻⁹ | 2.1 × 10⁻⁶ | 234.77 |
| Ag₂CrO₄ | 1.1 × 10⁻¹² | 4s³ | 6.5 × 10⁻⁵ | 2.2 × 10⁻² | 331.73 |
| Ag₂CO₃ | 8.1 × 10⁻¹² | 4s³ | 1.3 × 10⁻⁴ | 3.5 × 10⁻² | 275.74 |
| Ag₂SO₄ | 1.2 × 10⁻⁵ | 4s³ | 1.4 × 10⁻² | 4.5 × 10⁰ | 311.79 |
| Ag₃PO₄ | 8.9 × 10⁻¹⁷ | 27s⁴ | 4.3 × 10⁻⁵ | 1.8 × 10⁻² | 418.57 |
| BaSO₄ | 1.1 × 10⁻¹⁰ | s² | 1.0 × 10⁻⁵ | 2.4 × 10⁻³ | 233.38 |
| BaCO₃ | 5.1 × 10⁻⁹ | s² | 7.1 × 10⁻⁵ | 1.4 × 10⁻² | 197.34 |
| BaF₂ | 1.7 × 10⁻⁶ | 4s³ | 7.5 × 10⁻³ | 1.3 × 10⁰ | 175.32 |
| CaCO₃ (calcite) | 3.3 × 10⁻⁹ | s² | 5.7 × 10⁻⁵ | 5.7 × 10⁻³ | 100.09 |
| CaF₂ | 3.9 × 10⁻¹¹ | 4s³ | 2.1 × 10⁻⁴ | 1.7 × 10⁻² | 78.07 |
| CaSO₄ | 2.4 × 10⁻⁵ | s² | 4.9 × 10⁻³ | 6.7 × 10⁻¹ | 136.13 |
| Ca(OH)₂ | 6.5 × 10⁻⁶ | 4s³ | 1.2 × 10⁻² | 8.7 × 10⁻¹ | 74.09 |
| Ca₃(PO₄)₂ | 2.0 × 10⁻²⁹ | 108s⁵ | 7.1 × 10⁻⁷ | 2.2 × 10⁻⁴ | 310.17 |
| Mg(OH)₂ | 5.6 × 10⁻¹² | 4s³ | 1.1 × 10⁻⁴ | 6.5 × 10⁻³ | 58.32 |
| Fe(OH)₂ | 4.9 × 10⁻¹⁷ | 4s³ | 2.3 × 10⁻⁶ | 2.1 × 10⁻⁴ | 89.86 |
| Fe(OH)₃ | 2.8 × 10⁻³⁹ | 27s⁴ | 1.0 × 10⁻¹⁰ | 1.1 × 10⁻⁸ | 106.87 |
| Al(OH)₃ | 1.3 × 10⁻³³ | 27s⁴ | 2.6 × 10⁻⁹ | 2.1 × 10⁻⁷ | 78 |
| Cu(OH)₂ | 2.2 × 10⁻²⁰ | 4s³ | 1.8 × 10⁻⁷ | 1.7 × 10⁻⁵ | 97.56 |
| Zn(OH)₂ | 3.0 × 10⁻¹⁷ | 4s³ | 2.0 × 10⁻⁶ | 1.9 × 10⁻⁴ | 99.39 |
| Ni(OH)₂ | 5.5 × 10⁻¹⁶ | 4s³ | 5.2 × 10⁻⁶ | 4.8 × 10⁻⁴ | 92.71 |
| PbCl₂ | 1.7 × 10⁻⁵ | 4s³ | 1.6 × 10⁻² | 4.5 × 10⁰ | 278.1 |
| PbI₂ | 7.1 × 10⁻⁹ | 4s³ | 1.2 × 10⁻³ | 5.6 × 10⁻¹ | 461.01 |
| PbSO₄ | 2.5 × 10⁻⁸ | s² | 1.6 × 10⁻⁴ | 4.8 × 10⁻² | 303.26 |
| PbCrO₄ | 2.8 × 10⁻¹³ | s² | 5.3 × 10⁻⁷ | 1.7 × 10⁻⁴ | 323.19 |
| CuI | 1.3 × 10⁻¹² | s² | 1.1 × 10⁻⁶ | 2.2 × 10⁻⁴ | 190.45 |
| Hg₂Cl₂ | 1.3 × 10⁻¹⁸ | 4s³ | 6.9 × 10⁻⁷ | 3.2 × 10⁻⁴ | 472.08 |
| SrSO₄ | 3.4 × 10⁻⁷ | s² | 5.8 × 10⁻⁴ | 1.1 × 10⁻¹ | 183.68 |
These are typical textbook values. Published Ksp values vary by source, sometimes by a factor of 2 or more, especially for hydroxides and carbonates. CaCO₃ uses 3.3 × 10⁻⁹ (calcite); some textbooks list 4.5 × 10⁻⁹ or 8.7 × 10⁻⁹. PbI₂ uses 7.1 × 10⁻⁹; others give 9.8 × 10⁻⁹ or 1.4 × 10⁻⁸. Use the value from your course and type it into the Ksp box. Solubilities are calculated in pure water and ignore hydrolysis, complex ions and activity effects.
Worked examples
Solubility of AgCl
Ksp = 1.8 × 10⁻¹⁰ = s².
s = √(1.8 × 10⁻¹⁰). In g/L: 1.34 × 10⁻⁵ × 143.32
s = 1.34 × 10⁻⁵ M = 1.9 × 10⁻³ g/L
Solubility of CaF₂
Ksp = 3.9 × 10⁻¹¹ = (s)(2s)² = 4s³.
s = (3.9 × 10⁻¹¹ / 4)^(1/3)
s = 2.1 × 10⁻⁴ M, [F⁻] = 4.3 × 10⁻⁴ M
Ksp from solubility (NEET style)
The solubility of BaSO₄ is 2.4 × 10⁻³ g/L. M = 233.38 g/mol.
s = 2.4 × 10⁻³ / 233.38 = 1.03 × 10⁻⁵ M; Ksp = s²
Ksp = 1.06 × 10⁻¹⁰
Common-ion effect
Solubility of AgCl in 0.10 M NaCl.
s(s + 0.10) = 1.8 × 10⁻¹⁰, so s ≈ 1.8 × 10⁻¹⁰ / 0.10
s = 1.8 × 10⁻⁹ M (7500 times less than in water)
Precipitation check (AP style)
100 mL of 0.010 M Pb(NO₃)₂ is mixed with 100 mL of 0.010 M KI. Ksp(PbI₂) = 7.1 × 10⁻⁹.
After mixing [Pb²⁺] = [I⁻] = 0.0050 M. Q = (0.0050)(0.0050)² = 1.25 × 10⁻⁷.
Q greater than Ksp, so PbI₂ precipitates
Comparing solubilities (JEE trap)
AgCl (Ksp 1.8 × 10⁻¹⁰) vs Ag₂CrO₄ (Ksp 1.1 × 10⁻¹²). Which dissolves more?
AgCl: s = 1.3 × 10⁻⁵ M. Ag₂CrO₄: s = (1.1 × 10⁻¹² / 4)^(1/3) = 6.5 × 10⁻⁵ M.
Ag₂CrO₄ is more soluble despite its smaller Ksp
Common mistakes
- Forgetting the coefficients. For CaF₂, [F⁻] = 2s, and it is squared: Ksp = s(2s)² = 4s³, not s³ or 2s².
- Comparing Ksp across different formula types. A smaller Ksp only means lower solubility when the salts have the same x : y ratio. Compare molar solubilities instead.
- Ignoring dilution on mixing. Mixing equal volumes halves each concentration before you calculate Q.
- Salt vs ion concentration. 0.10 M CaCl₂ gives 0.20 M Cl⁻. 0.10 M Na₂SO₄ gives 0.10 M SO₄²⁻.
- Using the shortcut when it fails. If the common-ion concentration is not much larger than s, the approximation can be far off. Use the exact result.
- Hydrolysis and complexes. Carbonates, phosphates, sulfides and hydroxides are more soluble in acid. Excess Cl⁻ or NH₃ can dissolve AgCl as complex ions. These simple formulas ignore both.
Drawing ionic lattices or reaction schemes? MolDraw is a free online chemical structure editor for molecules, ions, reactions and lab diagrams.
Open MolDraw editorFrequently asked questions
How do I calculate molar solubility from Ksp?
Write the dissolution equation, express each ion as a multiple of s, and solve Ksp = xˣyʸ s^(x+y). For AgCl, s = √Ksp = √(1.8 × 10⁻¹⁰) = 1.34 × 10⁻⁵ M. For CaF₂, s = (Ksp/4)^(1/3) = 2.1 × 10⁻⁴ M.
How do I convert solubility in g/L to Ksp?
Divide by the molar mass to get mol/L, then use the Ksp expression. 2.4 × 10⁻³ g/L of BaSO₄ is 1.03 × 10⁻⁵ M, so Ksp = (1.03 × 10⁻⁵)² = 1.06 × 10⁻¹⁰.
What is the common-ion effect?
A salt is less soluble in a solution that already contains one of its ions, because the equilibrium shifts toward the solid (Le Chatelier). AgCl is about 7500 times less soluble in 0.10 M NaCl than in pure water.
How do I know if a precipitate will form?
Calculate the ion concentrations after mixing and the ion product Q = [M]ˣ[A]ʸ. If Q is greater than Ksp, a precipitate forms. If Q is less than or equal to Ksp, the solution stays clear.
Does a smaller Ksp always mean lower solubility?
Only for salts of the same type, such as two 1:1 salts. Ag₂CrO₄ has a smaller Ksp than AgCl but a higher molar solubility, because its Ksp contains 4s³ rather than s².
Why do Ksp values differ between textbooks?
Ksp values come from different measurements, temperatures and ways of correcting for ionic strength. Differences of a factor of 2 or more are common for hydroxides and carbonates. Use the value your course or exam gives.
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