Solubility Product (Ksp) Calculator: Solubility, Common Ion Effect and Precipitation

Solubility product questions solved with the working.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose the type of question and the formula type of the salt.

Enter Ksp, or the solubility, or the ion concentrations.

The calculator gives the solubility, the Ksp, the effect of a common ion, or whether the ion product Q passes Ksp.

Formulas used

  • K_{sp} = [A]^m[B]^n
  • s = \left(\frac{K_{sp}}{m^mn^n}\right)^{1/(m+n)}
  • Q > K_{sp}:\ \text{precipitate}

Worked example

With the default numbers in the calculator above:

  1. Dissolving equation and the Ksp expression: Ksp = [A]^1 [B]^1
  2. Molar solubility: [A] = ms and [B] = ns, so Ksp = m^m n^n s^(m+n): 1.3416e-5 mol/L
  3. Concentrations of the ions in a saturated solution: [A] = 1.3416e-5 mol/L, [B] = 1.3416e-5 mol/L

Change the numbers in the calculator to see the full working, every step, for your own case.

A second worked example

A different case, with these numbers: Formula type of the salt (cation then anion) AB2 (such as CaF2, PbCl2); The solubility product Ksp 3.9E-11.

  1. Dissolving equation and the Ksp expression: Ksp = [A]^1 [B]^2
  2. Molar solubility: [A] = ms and [B] = ns, so Ksp = m^m n^n s^(m+n): 2.1363e-4 mol/L
  3. Concentrations of the ions in a saturated solution: [A] = 2.1363e-4 mol/L, [B] = 4.2727e-4 mol/L

Common questions

What is the solubility product?

The equilibrium constant for a sparingly soluble salt dissolving. It is the product of the ion concentrations in a saturated solution.

What is the common ion effect?

A salt is less soluble in a solution that already contains one of its ions.

How do I tell if a precipitate will form?

Work out Q, the ion product with the concentrations after mixing. If Q is more than Ksp, a precipitate forms.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any first-year chemistry text (solubility equilibria).

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