Academic Chemistry
Mr. Gensits
Class Notes 9/28/2010
Mixtures
Mixture – a physical blend of two or more components
Most samples of matter are mixtures.
Heterogeneous Mixtures – the composition is not uniform throughout
Examples:
Granite
Vegetable Soup
Pond Water
Homogeneous Mixtures – the composition is uniform throughout
Examples:
Salt water
Air
Brass
Milk
Homogeneous mixtures are also called solutions.
Phase -any part of a sample with uniform composition and properties
All homogeneous mixtures consist of a single phase
Air has one phase
Oil and water has two phases.
Alloys – a mixture of two or more elements, at least one of which is a
metal
Examples:
Sterling silver – Ag, Cu
Cast iron – Fe, C
Stainless steel – Fe, Cr, C, (Ni), (Mo)
Bronze – Cu, Sn
Solute – substance being dissolved in a solution
Solvent – substance that dissolves the solute
In aqueous solutions the solvent is water.
Separating Mixtures
Differences in the physical properties of the components in a mixture
can be used to separate them from one another.
The easiest and most effective technique depends upon the physical
characteristics of the substances that make up the mixture.
Methods of Separating Mixtures
The following techniques can be considered when attempting to separate
a mixture:
1. Filtration - method used to separate a solid from a fluid. The
solid is separated when the mixture is placed on a medium that retains
the solid while allowing the fluid to pass through.
2. Decantation – technique that can be used to separate an insoluble
solid from a liquid. The liquid is carefully poured away leaving the
sediment behind.
3. Chromatography – a mixture is dissolved in a “mobile phase” which
passes over or through a “stationary phase.” The separation occurs due
to the relative affinities for the dissolved substances to the two
phases. Paper chromatography is often used to separate colored dyes in
a solution.
4. Fractional Crystallization - is a method of separating dissolved
solids due to their differences in solubility in the solvent. If two or
more substances are dissolved in a liquid, they will crystallize out of
solution at different rates at different temperatures depending on their
relative solubility.
5. Magnetism – a magnetic substance can be physically pulled out of a
mixture with a magnet.
6. Distillation – a dissolved solid and a liquid solvent can be separated
and isolated from each other by boiling away the solvent and condensing
the resultant vapor in a separate container.
7. Fractional Distillation – two liquids can be separated from one
another by using their boiling points. If the difference in the boiling
points of the two liquids is greater than 25oC then a simple distillation
may be employed.
8. Centrifugation – process that utilizes centrifugal force to separate
substances with different densities.