Variables
Description
What is this formula?
This formula calculates the molar solubility of a sparingly soluble salt from its solubility product constant.
When to use it
Use this equation when determining how much of a slightly soluble ionic compound can dissolve in pure water at equilibrium.
Example
For the salt MX:
MX ⇌ M+ + X−
Given:
Ksp = 4.0×10^-10
Formula:
s = √Ksp
Substitution:
s = √(4.0×10^-10)
Result:
s = 2.0×10^-5 mol/L
Applications
Solubility calculations
Precipitation analysis
Water chemistry
Environmental chemistry
Analytical chemistry
Note
This formula applies only to salts that dissociate in a 1:1 stoichiometric ratio, such as MX ⇌ M+ + X−. Salts with other stoichiometries, such as MX2, M2X3, or MX3, require different relationships between Ksp and molar solubility because the ion concentrations are not equal to the molar solubility. More general cases are usually treated separately in chemistry textbooks.