Solubility product (Ksp) & precipitation calculator

How to use (3 steps)

Pick a mode: Ksp → solubility, solubility → Ksp, Q vs Ksp (precipitation test), or simple fractional precipitation.
Enter the salt, stoichiometric coefficients, Ksp or solubility, and concentrations or volumes as needed.
Compute to see solubility, Ksp, Q vs Ksp, and interval summaries. Copy the URL to share the exact setup.

Default examples use classic salts such as AgCl and CaF2 so that you can compare textbook-style values before you compute.

Inputs

Choose a mode, adjust the example values, then compute or copy the URL. Units use mol/L and g/L for clarity.

Ksp → solubility Solubility → Ksp Precipitation test (Q vs Ksp) Fractional precipitation (simple)

Salt label

Cation coefficient ν_cation

Anion coefficient ν_anion

Molar mass of salt (g/mol, optional)

Ksp

Common anion [A⁻]₀ (mol/L, optional)

If you enter a common anion concentration (e.g. NaCl already present), the calculator solves the Ksp expression numerically for the new molar solubility.

Results

Mode: Ksp → solubility

How it's calculated

Choose a mode and compute to show the Ksp, Q, solubility, or fractional-precipitation steps for the current example.

Using the Ksp and precipitation modes

Use Ksp to solubility when you want the molar solubility of one salt in pure water. Use Q vs Ksp when you already know the mixed ion concentrations and need to decide whether a precipitate forms.

Suggested workflow

Choose the mode that matches your question before editing concentrations.
Enter stoichiometric coefficients exactly as written for the dissolving salt so the exponent pattern in Ksp is correct.
After computing, read both the summary and the step log to confirm which quantity the page solved for.

What the fractional-precipitation view assumes

The shared-anion view compares two salts against the same free anion concentration. It is useful for classroom selectivity problems, but it does not model activity coefficients, ionic-strength corrections, or complex side equilibria.

Common mistakes to avoid

Entering a concentration after mixing into the solubility mode, which expects Ksp and stoichiometry instead.
Forgetting that Q and Ksp use powers from the dissolution stoichiometry, not just a simple product of concentrations.
Comparing salts with different stoichiometries in the shared-anion range without checking whether the interpretation still matches your lesson.

FAQ

Does this tool account for activities and ionic strength?

For simplicity, it treats activities as equal to molar concentrations and does not include activity coefficients or ionic-strength corrections. It is meant for teaching-level Ksp and precipitation exercises, not for precise analytical calculations.

Which salts and stoichiometries can I use?

The core formulas accept general ν_cation and ν_anion coefficients (for example 1:2 salts such as CaF₂), as long as you provide the correct stoichiometric coefficients and Ksp values. For fractional precipitation, the built-in explanation assumes simple 1:1 salts with a shared anion.

Related calculators

Acid-base titration curve & pH
Compare equivalence-point chemistry when a precipitation question sits beside an acid-base lab workflow.
Acid-base titration curve simulator
Use this for quick volume-pH scenarios when you want a visual complement to the Q vs Ksp calculation.
Acid–base pH
Check how solution pH or dilution choices may shift the chemistry around your solubility worksheet.
Beer-Lambert law & calibration curve
Estimate dissolved concentrations from absorbance data before comparing ionic products with Ksp.
Buffer pH (Henderson-Hasselbalch)
Review buffer assumptions if your precipitation setup depends on a controlled acid-base environment.

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