Academic Chemistry
Mr. Gensits
Class Notes 3/11/2010
Separating Mixtures
Mixtures can be separated into their constituent substances
through physical means. There are many physical processes that
can be used to separate mixtures. The easiest and most
effective technique depends upon the physical characteristics of
the substances that make up the mixture.
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.