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
\(\begin{array}{l}S = \sqrt{K_{sp}}\end{array} \)

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.


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


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  1. Its really good and very helpful thank you for clearing my doubts

  2. Thanks so much for helping me to understand more better