Solutions

The Solution Process

Objectives1. 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

SolubilitySolution 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 SolventsImmiscible – 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.