Solubility and Temperature Effects in Solutions

Solubility and Temperature Effect

Introduction to Solubility

Solubility refers to the ability of a solute (such as a solid, liquid, or gas) to dissolve in a solvent to form a homogeneous solution. The solubility of substances is influenced by temperature, especially for solids and gases in liquids.

• Solute: The substance being dissolved.

• Solvent: The substance doing the dissolving, usually present in greater amount.

Types of Solutions Based on Solubility

• Unsaturated Solution: A solution that contains less than the maximum amount of dissolved solute at a given temperature. More solute can still be dissolved.

• Saturated Solution: A solution that contains the maximum amount of dissolved solute possible at a given temperature. Any additional solute will not dissolve.

• Supersaturated Solution: A solution that contains more dissolved solute than is normally possible at a given temperature. This is achieved by dissolving solute at a higher temperature and then cooling the solution carefully.

Example: If 100g of solute is dissolved in 100g of water at a certain temperature, and this is the maximum amount that can dissolve, the solution is saturated. If less than 100g is dissolved, it is unsaturated. If more than 100g is dissolved (by heating and then cooling), it is supersaturated.

Temperature Effect on Solubility

Temperature has a significant effect on the solubility of solids and gases in liquids:

• Solids in Liquids: Generally, the solubility of most solid solutes in a liquid solvent increases as temperature increases.

• Gases in Liquids: The solubility of gases in a liquid solvent decreases as temperature increases.

Equation for Solubility (General):

$\text{Solubility} = \frac{\text{mass of solute}}{\text{mass of solvent}}$

Application Example

Example: Caffeine is about 10 times as soluble in warm water as in cold water. If a student puts a hot-water extract of caffeine into an ice bath, some caffeine crystallizes. The identity of the solution before it is placed in an ice bath is supersaturated, because it contains more dissolved solute than is normally possible at the lower temperature.

Practice Question

In general, as the temperature increases, the solubility of gas in a given liquid decreases, and the solubility of most solids in a given liquid increases.

Summary Table: Temperature Effect on Solubility

Type of Solute	Effect of Increasing Temperature
Solid in Liquid	Solubility increases
Gas in Liquid	Solubility decreases