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[MUSIC PLAYING]

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[CHIMES]

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SARAH TOBACCO: Sublimation.

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The physical transformation
of a solid into a gas

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without intermediate
melting to the liquid

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is called sublimation.

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While this particular
phase transformation only

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occurs with solids that
have appreciable vapor

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pressure below the melting
point, in these cases,

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it can sometimes be used as
a purification technique.

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This video will illustrate
the atmospheric pressure

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sublimation of ferrocene.

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While sublimation can
also be carried out

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under reduced pressure, the
basic principles and steps

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are the same, so a reduced
pressure sublimation will not

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be demonstrated.

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Sublimation can occur when a
compound has appreciable vapor

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pressure below
its melting point.

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In certain cases,
sublimation can

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be used as a purification
technique in the laboratory.

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It only works when
a compound can

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undergo sublimation and
subsequent condensation

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without decomposition.

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It is also essential that none
of the impurities in the sample

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sublime under the
same conditions.

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And atmospheric pressure
sublimation setup

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is very simple.

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It consists of a hot plate,
the bottom of a culture

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dish containing the impure
sample, the lid of the culture

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dish, and an ice bath.

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It's really that simple.

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Start by transferring
your impure sample

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to the culture dish.

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Spread it out so that it is
no more than 5 millimeters

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thick at any point.

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Place the sample on the hot
plate and top it with the lid.

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Set the ice bath on the lid
and turn the heat on very low.

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Be patient,
sublimation takes time.

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[ALARM]

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GUEST SPEAKER:
Caution, overheating

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will destroy your material.

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But it's a good way
to make road tar.

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SARAH TOBACCO: With
a little patience

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and the right
conditions, you will soon

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observe formation of crystals
on the lid of the culture dish.

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Let a layer of crystals grow
and then turn off the heat.

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Let the setup cool down a
little bit before you gently

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slide the ice bath
off of the lid.

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[ALARM]

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GUEST SPEAKER: Caution,
if you're not careful,

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you'll lose your crystals.

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SARAH TOBACCO: Careful the lid
might stick to the bath which

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can be disastrous.

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If you were careful enough,
you can now lift the lid

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and see the layer of
beautiful, purified crystals.

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Scrape the crystals
into a clean watch glass

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and marvel over the
dramatic improvement

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over your initial sample.

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I know it doesn't look like a
lot of crystals, but remember,

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this is just the first batch.

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Replace the lid on the culture
dish, top it with the ice bath,

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and turn the heat
back on to harvest

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another batch of
beautiful crystals.

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Repeat these steps
until you have

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purified all of your compound.

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Remember, this video
is intended to help

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you prepare for lab by
providing a demonstration

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of the proper
experimental technique.

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It is not intended
as a replacement

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for reading your lab manual
or the supplementary material.

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In order to become a
great experimentalist,

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it is important that you
understand both theory

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and technique.

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Now it's your turn, good luck.

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