**Solubility Formula**

The term solubility is all about to measure the quantity of solute dissolved in a particular solvent. The simple definition of solubility is solubility of a substance is the molarity of that substance in a solution which is at chemical equilibrium under excessive undissolved substance. This states that there must be a uniform temperature throughout the system, since solubility is temperature dependent.**The Solubility Formula** can be mathematically expressed as

The expression for solubility product has the same general form than other equilibrium constant expressions and K_{SP} is called solubility product constant ”

**Example 1**

Determine the solubility of calcium fluoride C_{a}F_{2}

**Solution:**

The equilibrium for this salt is,

CaF_{2}(s) ⇋⇋ Ca+(aq) + 2F–(aq)

The K_{sp} expression is expressed as

K_{sp} = [Ca^{2+}][F–]^{2} = 4.0 times 10^{-11} M^{3}

Let S be the solubility of the Ca^{2+} ion

Then 2S is the solubility of the F– ion.

Substitute S in the K_{sp} expression, we get

(S)(2S)^{2} = 4.0 × 10^{11}

4S^{3} = 4 × 10^{11}

S = 2.15 ×10^{-4}M

** Example 2**

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 SnI_{2} is

SnI_{2}(s) ⇋⇋ Sn^{2}+(aq) + 2I–(aq)

The K_{sp} expression is written as

K_{sp} = [Sn^{2+}][I–]^{2}

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

[Sn^{2+}] = 1.28 × 10^{-2}M

[I^{–}] = (2) × 1.28 × 10^{-2}M

= 2.56 × 10^{-2}M

Substitute these values in K_{sp} expression

K_{sp} = (1.28 ×× 10-2M)(2.56 ×× 10-2M)2

Therefore, K_{sp} = 8.4 × 10-6 M^{2}