Solutions
The Solution Process
Objectives
1. Describe the factors that affect solubility and the
rate at which the solute dissolves.
2. Distinguish between saturated, unsaturated, and
supersaturated solutions.
Factors Affecting the Rate of Dissolution
1. Surface area
2. Stirring
3. temperature
Solubility
Solubility
Solution equilibrium – state in which dissolution and
crystallization of a solute occur at equal rates
Saturated solution – a solution that contains the
maximum amount of dissolved solute
Unsaturated solution – a solution that contains less
solute than the maximum that can be dissolved under
the existing conditions.
Supersaturated solution – a solution that contains
more dissolved solute than a saturated solution under
the same conditions.
Solubility Values
Solubility – amount of a solute that forms a saturated
solution in a given amount of solvent at a specific
temperature
• Pressure must be specified for gases
Examples: solubility in 100 g of H2O at 20oC
NaCl: 35.9 g
O2: 0.00537 g at 1 atm
Objectives
1. Describe the factors that affect solubility.
2. Describe the interactions that contribute to the
heat of solution.
Solute-Solvent Interactions
“Like
dissolves
Like”
Ionic Compounds in Aqueous Solutions
Hydration – process in
which water molecules
are attracted to ions in
solution.
Liquid Solutes and Solvents
Immiscible – when liquid solutes and solvents
are not soluble in each other
Miscible – when liquids dissolve freely in one
another.
Effects of Pressure
Gas + solvent ↔ solution
Henry’s Law
• The solubility of a gas
in a liquid is directly
proportional to the
partial pressure of that
gas on the surface of the
liquid
Effect of Temperature on Solubility
Heat of Solution
• The net amount of energy released or absorbed when
a specific amount of solute dissolves in a solvent.
-can be exothermic or endothermic
Heat of Solution
The heat of solution is the sum of the following energy
changes.
1. Solute particles must be separated.
Energy is required (lattice energy)
2. Solvent particles must be separated.
Energy is required (intermolecular forces)
3. Solute particles are attracted to solvent particles
(solvation)
Energy is released.