Mixtures & Solubility – Part I

Mixtures are a physical blend of at least two substances; have variable composition. They can be either: Heterogeneous – the mixture is not uniform in composition Chocolate chip cookie, gravel, soil. Homogeneous - same composition throughout; called “solutions” Kool-aid, air, salt water Every part keeps it’s own properties.

Phase? The term “phase” is used to describe any part of a sample with uniform composition of properties. A homogeneous mixture consists of a single phase A heterogeneous mixture consists of two or more phases.

Separating Mixtures Some can be separated easily by physical means: rocks and marbles, iron filings and sulfur (use magnet) Differences in physical properties can be used to separate mixtures. Filtration - separates a solid from the liquid in a heterogeneous mixture (by size)

Separation of a Mixture Components of dyes such as ink may be separated by paper chromatography.

Separation of a Mixture Distillation: takes advantage of different boiling points. NaCl boils at 1415 oC

Remember… all substances are either: a) elements, or b) compounds

Substances: element or compound Elements- simplest kind of matter cannot be broken down any simpler and still have properties of that element! all one kind of atom. Compounds are substances that can be broken down only by chemical methods when broken down, the pieces have completely different properties than the original compound. made of two or more atoms, chemically combined (not just a physical blend!)

Compound vs. Mixture Compound Mixture Made of one kind of material Made of more than one kind of material Made by a chemical change physical change Definite composition Variable

Understanding Solutions Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount

Mixtures & Solubility – Part II

Solvation Solvation – the process of dissolving solute particles are surrounded by solvent particles First... solute particles are separated and pulled into solution Then...

Recall the states of matter symbols… (s) = solid (l) = liquid (aq) = aqueous (made with water) (g) = gas

Solvation “Like Dissolves Like” NONPOLAR POLAR

Solvation Soap/Detergent polar “head” with long nonpolar “tail” dissolves nonpolar grease in polar water

Solubility UNSATURATED SOLUTION more solute dissolves no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Solubility Solubility maximum grams of solute that will dissolve in 100 g of solvent at a given temperature varies with temp based on a saturated soln

Solubility Solubility Curve shows the dependence of solubility on temperature

Solubility Rules 1. Higher temp. usually increases solubility 2. Higher pressure increases solubility of a gas 3. Polar solutes will dissolve in like polar solvents; nonpolar solutes will dissolve in nonpolar solvents