Calculator
Formula Used
For a sparingly soluble salt with the general form ApBq, the dissociation is written as:
ApBq(s) ⇌ pA + qB
If molar solubility is s, then cation concentration is p × s. Anion concentration is q × s. With activity factors and common ions:
Ksp = (γA × [A])p × (γB × [B])q
This calculator also adjusts mass based solubility by molar mass. Purity and dilution corrections are applied before ion concentrations are raised to their powers.
How to Use This Calculator
- Enter the salt name and ion labels.
- Add the cation and anion coefficients from the balanced equation.
- Enter solubility and select the matching unit.
- Provide molar mass when using mass based solubility.
- Adjust purity, dilution, activity factors, and common ions if needed.
- Press calculate to show Ksp above the form.
- Use CSV or PDF export for saving results.
Example Data Table
| Salt | Dissociation | Molar Solubility | Ksp Expression | Example Ksp |
|---|---|---|---|---|
| AgCl | AgCl ⇌ Ag+ + Cl- | 1.30E-5 mol/L | [Ag+][Cl-] | 1.69E-10 |
| CaF2 | CaF2 ⇌ Ca2+ + 2F- | 2.10E-4 mol/L | [Ca2+][F-]2 | 3.70E-11 |
| PbCl2 | PbCl2 ⇌ Pb2+ + 2Cl- | 1.60E-2 mol/L | [Pb2+][Cl-]2 | 1.64E-5 |
Article: Calculating Ksp From Solubility
Why Ksp Matters
Ksp describes how much of an ionic solid can dissolve. It is called the solubility product constant. A small value means the salt dissolves only slightly. A larger value means more ions can remain in solution. This value helps in chemistry, water testing, lab reports, and product quality checks.
Solubility and Ion Balance
The key step is the balanced dissociation equation. Each dissolved formula unit creates ions in fixed ratios. AgCl gives one silver ion and one chloride ion. CaF2 gives one calcium ion and two fluoride ions. Those coefficients become powers in the final expression.
Using Molar Solubility
Molar solubility is the easiest input. It tells moles dissolved per liter. When solubility is entered as mass, the calculator converts it with molar mass. It also supports grams per liter, milligrams per liter, grams per hundred milliliters, and milligrams per hundred milliliters.
Corrections and Activity
Real samples may need corrections. Purity changes the true dissolved amount. Dilution changes the original concentration. Common ions increase the final ion concentration. Activity factors improve estimates when solutions are not ideal. These options make the calculator useful for simple lessons and advanced lab work.
Reading the Result
The result table shows corrected molar solubility, ion concentrations, activities, Ksp, log value, and pKsp. Scientific notation keeps very small values readable. The export buttons help save the calculation for notes, reports, worksheets, or repeat analysis. Always match the ion coefficients with the real formula. A wrong coefficient gives a wrong power and a wrong Ksp.
Best Practice
Use reliable solubility data. Enter the molar mass for the exact solid, including hydrates when present. Keep temperature consistent because Ksp changes with temperature. For classroom work, activity factors of one are usually acceptable. For stronger solutions, corrected activities may give better chemical meaning.
FAQs
What is Ksp?
Ksp is the solubility product constant. It measures the ion product for a saturated solution of a sparingly soluble salt.
Can I use grams per liter?
Yes. Select a mass based unit and enter molar mass. The calculator converts the value into molar solubility before calculating Ksp.
Why are coefficients important?
Coefficients define ion amounts and powers. For CaF2, fluoride is doubled, so its concentration is squared in the Ksp expression.
What does purity percent do?
Purity corrects measured solubility for impure samples. A 95 percent sample uses only 95 percent of the entered mass value.
What is a dilution factor?
A dilution factor scales the measured concentration back to the original sample. Use 1 when no dilution correction is needed.
Should activity factors always be used?
For basic problems, use 1. For more advanced work, activity factors can improve estimates in non ideal ionic solutions.
What are common ion inputs?
Common ion inputs represent ions already present before dissolution. They are added to the ion concentration formed by the salt.
Why does temperature matter?
Ksp changes with temperature. The temperature field records your condition, so results remain easier to compare and document.