Unit 3: Solutions

Solutions

•A solution is a homogeneous mixture of at least two different compounds

•A solvent is any substance that has other substances dissolved in it

•Solutes are substances that are dissolved in the solvent

Solutions

•Liquids that dissolve easily in one another are called miscible with each other▫Example: water and ethanol

•Liquids that do not dissolve easily in one another are called immiscible▫Example: water and oil

• In an aqueous solution water is the solvent▫Water is also called a ‘universal solvent’

• In a saturated solution no more solute will dissolve

•An unsaturated solution is not saturated (you can dissolve more solute)

•Super saturated solution: a solution that contains more dissolved solute than a saturated solution at the same temperature and pressure.

Why Do Solutions Form?

3 forces must be considered

1. Forces that attract particles of the solute to each other.

2. Forces that attract particles of solute to the solvent

3. Forces that attract particles of solvent to each other.

2 ≥ 1 and 3

*Ethanol mixing with water

Solubility•Solubility is a measure of how much

solute will dissolve in a given amount of solvent at a particular temperature

•For (most) solids:▫Solubility ↑ with Temperature

•For (most) gasses:▫Solubility ↓ as Temperature ↑▫Solubility ↓ as Pressure ↓

Rate of Dissolving

•In general, the rate of dissolving increases with:

▫Temperature▫Stirring or swirling▫Smaller particle size (eg, crushing a solid into a powder)

Dissolving a Solid in a Liquid•Dissolving is not a chemical reaction

•Step 1:▫ Forces between particles in a solid must

be broken (requires energy)•Step 2:

▫Intermolecular forces in the liquid must be broken (requires energy)

•Step 3:▫Particles of the solid are attracted to

particles of the liquid (gives off energy)

Dissolving a Solid in a Liquid

•Steps 1 and 2 are endothermic (heat is absorbed)

•Step 3 is exothermic (heat is given off)

•Polarity affects solubility

Solvation

The process by which solvent molecules surround and interact with solute ions or

molecules.

Homework

•Make Notes: pg 360 – 369

•Do homework questions: •Pg 357 Q 3, 6 •pg 370 Q 2, 3, 4, 7, 13