Solubility

Solubility

What is solubility?

Solubility is the amount of a substance (solute) that dissolves completely in water (or another solvent) to form a solution with free ions.

Units of solubility

1. Solubility is often expressed in grams per liter (g/L) or grams per decimeter cubed (g/dm³).
2. When expressed in moles per liter (mol/L) or moles per decimeter cubed (mol/dm³), it is referred to as molar solubility.

Molar solubility

Definition: Molar solubility is the amount of solute (in moles) that dissolves in a given volume of solvent (1 dm³ or 1 liter) to give free ions in the solution.

Units:

1. When expressed in g/L, solubility represents the concentration of the solute in grams per unit volume.
2. When expressed in mol/L, it represents molar solubility, which is the same as molarity.

Examples of solubility calculations

1. Sodium hydroxide (NaOH)

Given Data:

Molar solubility = 0.0004 mol/dm³

Molar mass (M_r) = 40 g/mol

Solution:

Solubility = Molar solubility × Mr
Solubility = 0.0004 × 40 = 0.016 g/L

Result: The solubility of NaOH is 0.016 g/L.

2. Calcium hydroxide Ca(OH)₂

Given Data:

Molar solubility = 2.7 × 10-3 mol/dm³

Molar mass (M_r) = 74 g/mol

Solution:

Solubility = Molar solubility × Mr
Solubility = 2.7 × 10-3 × 74 = 0.1998 g/L

Result: The solubility of Ca(OH)₂ is 0.1998 g/L.

3. Sodium chloride (NaCl)

Given Data:

Solubility = 3.24 g/L

Molar mass (M_r) = 58.5 g/mol

Solution:

Molar solubility = Solubility in g/L ÷ M_r

Molar solubility = 3.24 ÷ 58.5 = 0.0554 mol/dm³

Result: The molar solubility of NaCl is 0.0554 mol/dm³.