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[MUSIC PLAYING]

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PROFESSOR: While working
in the laboratory,

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you will often be required
to separate liquid mixtures

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or to purify liquid from
non-volatile substances.

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This separation and
purification can

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be done by utilizing the
liquid's boiling point

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through a technique
called distillation.

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Distillation works through
the processes of vaporization

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and condensation.

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Vaporization is
the transformation

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of a liquid to a
gas, and condensation

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is the conversion of a
gaseous species into a liquid.

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To perform a distillation, a
mixture of two miscible liquids

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is heated until the liquid
with the higher vapor

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pressure reaches
its boiling point.

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This vapor travels up
the inside of the flask,

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through a distilling head,
and into a condenser.

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The cold water jacket
on the condenser

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transforms the vapor back into
liquid, which then travels

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into the receiving flask.

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In this manner,
distillation effectively

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separates lower
boiling point compounds

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from higher boiling
point compounds.

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Three types of
distillations are commonly

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used in the laboratory.

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Depending on your
liquid solution,

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you will have to decide
which type of distillation

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will be the most effective.

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The first type of distillation
is a simple distillation.

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This technique is used when
separating miscible liquids

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that boil below
150 degrees Celsius

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at 1 atmosphere from either
non-volatile impurities

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or from a second liquid that
boils at least 25 degrees

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Celsius higher than the first.

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The second type of distillation
is the fractional distillation.

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This technique should be used
to separate liquid mixtures that

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have less than a
25 degree Celsius

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difference in boiling point.

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The third type of distillation
is a vacuum distillation.

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This technique should be used
to separate miscible liquids

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that boil above 150 degrees
Celsius at 1 atmosphere.

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In this video,
"Distillation Part 1,"

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we will discuss simple and
fractional distillations.

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In "Distillation
Part 2," we will

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discuss vacuum distillations.

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To carry out a
simple distillation,

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you will need a cork ring,
a round bottom distilling

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flask, two ring stands, a
stir bar and magnetic stirrer,

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a distilling head, a condenser,
a vacuum adapter, grease,

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3 yellow keck clamps, a
thermometer and thermometer

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adapter, 3 round bottom
receiving flasks,

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2 extension clamps and
fasteners, a heating mantle,

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an iron ring, a variable
voltage transformer, or Variac;

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3 hose clips, 2 pieces
of rubber tubing,

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and a container for
an ice water bath.

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The first step in
performing a distillation

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is choosing the proper
sized distillation flask.

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The distilling flask should
not be more than 1/2 full

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or less than 1/3 full when
the distillation begins.

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If the flask is
overfilled, the solution

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will likely overheat or
bump into the condenser.

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Bumping will cause impurities
to be collected in the receiving

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flask, rendering the
distillation worthless.

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If the flask is
less than 1/3 full,

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then you'll have
a greater chance

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of losing some product
because a substantial amount

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of the material will be
needed just to fill the flask

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and distilling head with vapor.

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While we're on
the topic of size,

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we'd like to speak briefly
about heating mantles.

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If you do not have an
appropriately sized heating

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mantle, then use
one that is too big.

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Never use a heating mantle
that is too small because heat

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is not easily transferred
between the mantle

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and flask due to
poor contact, which

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causes the mantle to burn out.

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If the mantle is too
big for the flask,

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then add sand to fill
in the empty space.

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After you have chosen
a distilling flask,

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transfer your sample into it
and add an appropriately sized

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stir bar.

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If you will not have access
to a magnetic stirrer,

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then add a few boiling stones
to the distilling flask instead.

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The next step is the assembly
of the distillation apparatus,

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which is likely one of the most
difficult glassware assemblies

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you'll ever encounter.

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The neck of the
distilling flask is

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clamped onto one
of the ring stands

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with an extension
clamp and fastener.

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A heating mantle, which is
plugged into the Variac,

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rests on an iron ring
below the distilling flask.

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If you're using a stir bar,
then place a magnetic stirrer

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underneath the heating mantle.

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Leave enough room
below the iron ring

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so that the heating
mantle can be dropped away

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from the distilling
flask if necessary.

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The distilling head
is attached to the top

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of the distilling
flask, and a condenser

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is attached to the side
arm of the distilling head.

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The vacuum adapter is
attached to the other end

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of the condenser, and this joint
is attached to the second ring

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stand with an extension
clamp and fastener.

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A small receiving flask is
clamped to the vacuum adapter

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with the yellow keck clamp,
and an ice water bath

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is placed underneath.

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The thermometer and
thermometer adapter

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are attached to the top
of the distilling head

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and clamped in place with
the green keck clamp.

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The top of the
thermometer bulb should

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be aligned with the
bottom of the side arm

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on the distillation head.

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Yellow keck clamps
are used to secure

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both ends of the condenser.

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Rubber tubing is attached
to the water inlet

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and outlet of the condenser
and secured with hose clips.

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Finally, place 2
clean, dry receiving

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flasks near the
distillation apparatus.

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Before continuing, confirm
that all of the joints

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have been lightly
greased and that no keck

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clamps are used on any
joint that will become hot.

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After assembling the
distillation apparatus,

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attach the tubing at the
bottom of the condenser

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to the water source, place
the end of the tubing

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at the top of the
condenser into a sink.

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Remember, water goes
in at the bottom

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and out at the top to discourage
the formation of air bubbles.

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Double check that
all of the joints

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are secured with hose clips
and start the water flow.

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The water should
flow at the slowest

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rate that is necessary to
keep the condenser cold.

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If the flow rate is
too fast, the chance

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of the tubing popping off
the condenser and spring

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all over your workspace
greatly increases.

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To perform this
simple distillation,

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turn on the Variac and heat
the sample to a gentle boil.

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Make sure that the vacuum
adapter remains to the air.

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Never heat a closed
system, or it will explode.

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A ring of condensate
will move up the flask

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and into the distilling head.

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When the vapor reaches the
height of the thermometer bulb,

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the temperature reading
will jump dramatically,

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indicating the formation
of a droplet of liquid

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on the thermometer bulb.

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If the condensate
ring completely

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stops rising at any point,
slightly increase the setting

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on the Variac.

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After the vapor
reaches the condenser,

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it transforms back into liquid,
flows down the condenser

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and into a small
receiving flask.

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When approximately 10
drops have been collected

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in the small receiving
flask, quickly

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replace it with the larger one.

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The first couple of
drops of a distillation

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are always discarded because
they may contain some lower

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boiling impurities.

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At this point, the
distillate should

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be dropping into
the receiving flask

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at a rate of 10
drops per minute.

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If the rate is faster,
then the heat is too high,

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and higher boiling
point impurities

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may have escaped into
the receiving flask.

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If the rate is too slow,
then the distillation

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will occur over too
long of a time period.

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After the lower boiling liquid
has been completely distilled,

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no drop of liquid will be
on the thermometer bulb,

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and the temperature will
plunge dramatically.

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At this point, immediately
replace the large receiving

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flask with a new,
small receiving flask

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to collect the last
few drops of liquid.

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These drops may contain some
higher boiling impurities

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that should not be collected
in the main receiving flask.

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Record the temperature range
of when the mixture first

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started to boil until right
before the dramatic drop

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in temperature.

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This is the boiling
point of the distillate.

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If the range is within
2 degrees Celsius,

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your distillate is fairly pure.

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After you have collected the
final few drops of liquid,

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turn off the heat source.

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A simple distillation
is performed

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more effectively if certain
guidelines are followed.

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First, make sure all the joints
on the apparatus are tight

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and that the water
lines are secured.

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Second, fill the distilling
flask between 1/3 and 1/2

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full prior to distillation.

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Third, allow the
distillation to proceed

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at a rate of 10
drops per minute.

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Fourth, use separate
receiving flasks

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for the beginning, middle,
and end of the distillation

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to disallow low and high boiling
impurities into the distillate.

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Fifth, never let the
distillation flask run dry.

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A flask that is allowed to run
dry may overheat and break.

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The second type of
distillation that we will cover

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is the fractional distillation.

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This technique
should be used if you

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need to separate
two liquids that

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have a small difference
in boiling point--

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less than 25 degrees Celsius.

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Fractional distillation is more
effective at separating liquids

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with similar boiling
points because it utilizes

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a fractionating column.

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A fractionating column
contains column packing

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with a large surface
area and works

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by promoting a lot
of tiny distillations

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on the surface of this packing.

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Specifically, when the liquid
mixture is heated to boiling,

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the resulting vapor is richer
in the lower boiling component.

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The vapor moves out of
the flask and condenses

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on the bottom few centimeters
of the fractionating column.

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Now the condensed
droplet is richer

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in lower boiling
component, and the liquid

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in the distilling flask
is richer in the higher

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boiling component.

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If that liquid
droplet is reheated,

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it will vaporize and
condense a little further

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up the fractionating column.

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This distillate will have
an even higher percentage

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of the lower boiling component.

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This process is repeated
until the vapor reaches

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the top of the fractionating
column, where theoretically, it

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should be pure in lower
boiling component.

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To assemble the apparatus for
our fractional distillation,

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place a fractionating column
between the distillation flask

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and the distillation head.

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Alternatively, your lab may
have all-in-one distillation

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glassware that contains
a fractionating column.

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Perform the fractional
distillation

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in the same manner as
the simple distillation.

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To ensure an effective
fractional distillation,

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heat the distilling
flask very slowly.

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Too much heat causes
the distillation

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to occur too rapidly,
disallowing the liquid vapor

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equilibria on the surface
of the fractionating column.

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If too little heat is
used, then the column

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may lose heat faster than it
can be warmed up by the vapor,

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preventing the vapor from
reaching the top of the column.

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If the column seems to
be losing heat faster

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than it can be warmed
up by the vapor,

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you may insulate the column by
wrapping it with glass, wool,

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or cotton and aluminum foil.

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As a general rule, a
slow steady distillation,

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where one drop is collected
every 2 to 3 seconds,

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is reasonable.

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Distillation is an
effective technique

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for separating
impure fine liquids.

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When used correctly, pure
contents and good yields

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are readily attained.

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