 # Solubility Formula

The word solubility is all about calculating the amount of solute dissolved in given solvent. The simple concept of solubility of a substance is the molarity of the material under excessive undissolved material in a solution at chemical equilibrium. Since the solubility is temperature-dependent there should be uniform temperature throughout the system.  The solubility formula is expressed as

The expression for solubility product has the same general form than other equilibrium constant expressions and KSP is called solubility product constant ”

Example 1

The molar solubility of tin iodide SnI2 is 1.28 x 10-2 mol/L. Calculate the Ksp of this compound.

Solution:

The solubility equilibrium of SnI2 is

SnI2(s) Sn2+(aq) + 2I(aq)

The Ksp expression is written as

Ksp = [Sn2+][I]2

1 mol of SnI2 Produces 1.0 mol of Sn2+, but 2.0mol of I.

[Sn2+] = 1.28 × 10-2M

[I] = (2) × 1.28 × 10-2M

[I] = 2.56 × 10-2M

Substitute these values in Ksp expression

Ksp = (1.28 ×× 10-2M)(2.56 × 10-2M)2

Therefore, Ksp = 8.4 × 10-6 M2