Shrinithi Mahadevan


Solubility Product Constant Study Guide

The solubility water constant can be defined as an equilibrium constant for a solid substance that can get dissolved in an aqueous solution.


Have you ever wondered how the solid cubes of sugar dissolve so quickly in water? The solid cubes break down into individual molecules and are separated by the water molecules surrounding them. The solubility of a substance can be defined as the property of solute to dissolve in a solvent to form a solution. Every solvent has a solubility product, notated as Kₛₚ.


The solubility product constant, or Ksp, is an equilibrium constant of a solute that can dissolve easily in a solvent, for example, dissolving a sugar cube in water. In this scenario, the glucose that makes up the sugar is the solute, and the water is the solvent. As we mix them together, the glucose particles completely dissolve in water. Ksp is the constant number that describes the molar changes that occurred with the dissolution of glucose in water. Let’s take a look at an example of an aqueous solution:

bB (s) ⇆ eE (aq) aA (aq)


B = Solid

E, A = aqueous medium after the solid dissolves in it

We can find out the value of Ksp by multiplying the product if the molarities of the products. If there are coefficients present in the product, then we need to raise the product to the power of the coefficient and then multiply them to get the Kₛₚ. So,

Kₛₚ = [E]e x [A]a

Here, you will not find bB, as solid is not calculated in Kₛₚ. Hence, the solubility product constant can only be calculated in the aqueous medium.

Calculation of Solubility Product from Solubility Data Source


Natural sources of water have a high concentration of metal cations. These metals cations are toxic to humans and thus make the water unsuitable for drinking. To overcome this problem, many countries use advanced technology to filter these heavy metals from the water. Others without access to such technology use a different but still effective method: seashells.

66.70% of a seashell is composed of aragonite, a form of calcium carbonate (CACO3). Seashells help clean water by swapping calcium atoms with heavy metals, effectively filtering the water by locking them into a solid form.

Water purification by seashells Source


1. How do you find the solubility product constant Kₛₚ?

The solubility product constant Ksp is the equilibrium constant for a solid substance that dissolves in a liquid or aqueous medium. The more soluble the solid is, the higher will be its Kₛₚ value.

2. How is solubility related to Kₛₚ?

Ksp is the product of each ion in moles per liter. The relation of solubility and the solubility product constant is used to find the value of each other through the formation of the equation.

3. What is Kₛₚ equal to?

Kₛₚ = product of ions

4. What is the relationship between the solubility product constant Kₛₚ and temperature?

The solubility product Ksp increases with the increase in temperature. The increase in temperature will help the solute to break down and dissolve in the solvent faster. Hence, the Ksp increases with the temperature increase.

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  1. Water Purification with Seashell: Accessed 28 Feb 2022.
  2. Solubility Product Constant: Accessed 28 Feb 2022.