Ksp From Solubility Calculator

Calculator Form

Salt formula or name

Cation label

Anion label

Cation coefficient

Anion coefficient

Solubility value

Solubility unit

Molar mass, g/mol

Common cation, mol/L

Common anion, mol/L

Cation activity coefficient

Anion activity coefficient

Trial cation for Q, mol/L

Trial anion for Q, mol/L

Temperature note, °C

Significant figures

Formula Used

For a salt written as A_aB_b, the dissolution form is:

A_aB_b(s) ⇌ aA + bB

Molar solubility is represented by s.

[A] = [A]_common + a × s

[B] = [B]_common + b × s

Ksp = (γ_A[A])^a × (γ_B[B])^b

Use γ = 1 for a normal concentration based result.

How To Use This Calculator

Enter the compound label, cation label, and anion label.
Enter the ion coefficients from the balanced dissolution equation.
Add solubility and select its unit.
Enter molar mass when using g/L, mg/L, or g/100 mL.
Use zero common ions for pure water solubility.
Keep activity coefficients at one unless lab data gives them.
Add trial ion values when checking precipitation.
Press calculate, then export the result if needed.

Example Data Table

Compound	Dissolution ratio	Molar solubility	Approximate Ksp
AgCl	1:1	1.34E-5 mol/L	1.80E-10
CaF2	1:2	2.05E-4 mol/L	3.45E-11
PbI2	1:2	1.37E-3 mol/L	1.03E-8
Mg(OH)2	1:2	1.71E-4 mol/L	2.00E-11

Understanding Ksp From Solubility

Ksp links a solid salt to the ions it releases at equilibrium. It is useful when a compound dissolves only slightly. The value shows how much ion product can exist before extra solid remains. A small value means low solubility. A larger value means more dissolved ions.

Why Stoichiometry Matters

Solubility is often reported as one amount for the whole formula unit. Ksp uses ion concentrations instead. That means each coefficient changes the final value. For AgCl, one mole gives one silver ion and one chloride ion. So Ksp equals s squared. For CaF2, one mole gives one calcium ion and two fluoride ions. So Ksp equals s times two s squared. This difference is important.

Mass Solubility Conversion

Many tables give solubility in grams per liter or milligrams per liter. The calculator converts those values into molar solubility by using molar mass. When the unit is grams per one hundred milliliters, the value is first changed to grams per liter. Then it is divided by molar mass. Molar units can be used directly.

Common Ion Adjustment

A common ion changes equilibrium concentrations. If chloride is already present, AgCl dissolves less. When measured solubility is entered for that solution, the common ion amount is added to the ions made by the salt. This produces an apparent Ksp from the provided conditions. Pure water work should use zero common ions.

Activity Option

Advanced work may use activity coefficients. These values correct concentration for non ideal behavior. The calculator multiplies each ion concentration by its coefficient before raising it to the correct power. Use one when activity data is unknown. Use measured coefficients for higher level lab reports.

Practical Use

Ksp helps compare salts, predict precipitation, and check lab results. It also supports water treatment, qualitative analysis, and environmental chemistry. Good inputs matter. Confirm the formula coefficients. Use the correct molar mass. Match solubility units carefully. Review the log value when numbers are very small. It makes comparison easier and cleaner.

Interpreting Results

Ksp has units that depend on the balanced dissolution equation, yet many tables omit units. Keep the calculated expression visible. It helps readers see every exponent and concentration term clearly during review and classroom checking.

FAQs

What is Ksp?

Ksp is the solubility product constant. It describes the ion product for a sparingly soluble salt at equilibrium. It is based on ion concentrations raised to their stoichiometric powers.

Is molar solubility the same as Ksp?

No. Molar solubility is the dissolved amount of the whole salt. Ksp is calculated from the ion concentrations produced by that dissolved amount.

Why do coefficients affect the answer?

Coefficients show how many ions form from each formula unit. They change both concentration multipliers and exponents in the Ksp expression.

When should I enter molar mass?

Enter molar mass when solubility is given as g/L, mg/L, or g/100 mL. The calculator needs it to convert mass solubility into mol/L.

What should I enter for pure water?

Use zero for both common ion fields. That keeps the calculation based only on ions released by the dissolving salt.

What are activity coefficients?

Activity coefficients adjust concentrations for non ideal solutions. Leave them as one for standard concentration calculations unless your lab data provides better values.

Can this calculator check precipitation?

Yes. Enter trial cation and anion concentrations. The tool compares Q with Ksp and reports whether the mixture is unsaturated, near equilibrium, or supersaturated.

Why is log Ksp included?

Ksp values can be very small. The log value makes comparison easier, especially when studying several salts with very different solubilities.