Enter the solubility product constant (Ksp), molar solubility, and the ion stoichiometric coefficients into the calculator to determine the missing value (Ksp or molar solubility).

Molar Solubility Calculator

Ksp & Molar Solubility
Mass Solubility

Enter the ion coefficients and either Ksp or molar solubility to calculate the other.

Related Calculators

Molar Solubility Formula

The following formula is used to calculate the molar solubility of a sparingly soluble ionic compound in pure water (at a fixed temperature) from the solubility product constant and the stoichiometric coefficients of the dissolved ions.

S = (Ksp / (a^a * b^b))^(1/(a + b))

Variables:

  • S is the molar solubility (mol/L)
  • Ksp is the solubility product constant (commonly treated as unitless as an equilibrium constant; the concentration-form has units of (mol/L)(a+b))
  • a is the stoichiometric coefficient of ion 1 produced when the salt dissolves (e.g., CaF₂ → 1 Ca2+ so a = 1)
  • b is the stoichiometric coefficient of ion 2 produced when the salt dissolves (e.g., CaF₂ → 2 F− so b = 2)

To calculate the molar solubility, divide Ksp by aabb, then take the (a + b)th root. For a 1:1 salt (a = 1 and b = 1), this reduces to S = √Ksp.

What is Molar Solubility?

Molar solubility is a measure of the amount of a solute that can dissolve in a given volume of solvent to form a saturated solution. It is expressed in moles per liter (mol/L). For a simple sparingly soluble salt dissolving in pure water at a given temperature, the molar solubility is related to the solubility product constant (Ksp) and the dissolution stoichiometry (the ion coefficients). In real solutions, factors like common ions, complexation, and ionic strength can change the solubility from the pure-water value.

How to Calculate Molar Solubility?

The following steps outline how to calculate the Molar Solubility.

  1. First, determine the solubility product constant (Ksp) for the salt (at the temperature of interest).
  2. Next, determine the stoichiometric coefficients of the ions produced when the salt dissolves (a and b).
  3. Next, calculate the molar solubility using the formula S = (Ksp / (aa · bb))1/(a+b).
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Solubility Product Constant (Ksp) = 1.0 x 10-10

Coefficient of Ion 1 (a) = 1

Coefficient of Ion 2 (b) = 1