Question

What is the $Ksp$ equation?

Answer 1

The solubility product is the maximum product of the ionic concentrations or activities of an electrolyte that at one temperature can continue in equilibrium with the undissolved phase. We calculate the solubility product by taking the solid's solubility expressed in units of moles per liter, known as its molar solubility.

Complete answer:
The solubility product constant,$Ksp$​, is the equilibrium constant for a solid substance dissolving in an aqueous solution. It represents the level at which a solute dissolves in solution. The more soluble a substance is, the higher the$Ksp$ value it has.
Consider the general dissolution reaction below:
$aA \rightleftharpoons cC + dD$
To solve for the $Ksp$ it is necessary to take the molarities or concentrations of the products and multiply them. If there are coefficients in front of any of the products, it is necessary to raise the product to that coefficient power and also multiply the concentration by that coefficient. This is shown below:
$Ksp = [C]c[D]d$

Additional information:
Factors affecting solubility:

Temperature: Basically, solubility increases with temperature.
Polarity: In most cases solutes dissolve in solvents that have a similar polarity.
Pressure
Molecular size.
Stirring increases the speed of dissolving.

Note:
Remember that the reactant, $aA$, is not included in the $Ksp$ equation. Solids are not included when calculating equilibrium constant expressions, because their concentrations do not change the expression; any change in their concentrations are insignificant, and therefore omitted. Hence, $Ksp$ represents the maximum extent that a solid can dissolve in solution.