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Physical separations.

• There are several techniques which we use in a chemistry lab to separate mixtures.

• We will look at several in our Grade 10 course

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Let us start with simple filtration

The sieve is a crude filtration apparatus but using the coffee filter makes it better.

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Filtrate goes through the filter paper.

The residue get trapped by the filter paper

residue

filtrate

The usual set up for filtration

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Suction filtration

This method is faster once it is set up because a water pump sucks out the air beneath the filter paper

CHROMATOGRAPHY

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The dyes stick and unstick to the paper many thousands of times as they move up the paper. The difference in ‘stickyness’ separates the dyes.

PHYSICAL SEPARATIONS

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Chromatography

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At the start the dyes are placed in the solvent in a closed container

The chromatogram at the end of the run. The sovent front is marked with a pencil

Chromatography

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This is what it may look like whilst the solvent front rises up the paper. One doesn’t always need expensive apparatus!

The results can look complicated

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BUT, with the help of Rf values we can simplify them

Rf Values

• An Rf value is the distance travelled by the dye or spot divide by the distance travelled by the solvent.

• Since the solvent always goes higher the Rf value is less than 1

• If two dyes of the same colour have the same Rf value, then it is the same dye.

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Really simple distillation

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Simple distillation

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OTHER VERSIONS of SIMPLE DISTILLATION

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FRACTIONAL DISTILLATION

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Fractional distillation

This differs from simple distillation by using a fractionating column between the flask and the cold water condenser.

It may be used to separate liquids with closer boiling points

Fractional distillation

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This is what an industrial version looks like on the inside

CENTRIFUGE (The spinning machine)

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Using a separating funnel

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This is used to separate liquids which do not mix by pouring off the separate liquids

More separating funnels

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MAGNETIC SEPARATIONS

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Using sublimation

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Using sublimation

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An experiment using a piece of air freshener