>> host: Welcome back
to "Chemistry Matters."
With all we've learned so far
about matter's physical
and chemical properties,
and how different types
of matter mix together,
you're ready to learn
how to separate the chemicals
in those mixtures.
So, let's get back
to our classroom
and see how our students
are using physical properties
to separate chemicals.
>> professor: These bowls of
candy can be a great model
for separating water
from other materials
in a mixture.
Go ahead and separate
the purple pieces of candy.
We'll pretend they're
water molecules.
The other colors represent
all the other things that
might be mixed in the water.
If we remove all
the purple candies
and put them in one pile,
you'll see that the other pile
has all the other colors in it.
Those could be sand, dirt,
trash, and all the other stuff
you find in water.
They're all mixed together.
All the pure water
has been separated out.
In some water solutions, though,
we can't simply
reach our fingers in
and pull molecules out
one by one.
But, because we understand
the physical properties
of water, we can indeed
separate water safely.
>> student: Can all mixtures
be easily separated?
>> professor: Good question.
It depends on the mixture.
Some mixtures,
like drum cymbals,
are difficult to separate
without high-temperature melting
and industrial processes.
But as for mixtures that
can be easily separated,
let's take a look at
this sand and iron mixture.
Using the magnetic
physical properties
of iron filings,
try to use these magnets here
to separate out
the iron filings.
>> student: Oh,
that's pretty cool.
>> professor: Because
the mixtures are made up
of substances that
combine physically,
we can use physical processes
to separate mixtures.
Check this out.
Since liquids can have
different densities,
as you see in this
combination of red water
and yellowish vegetable oil,
it's pretty easy
to separate the oil,
which floats on top,
from the water,
because it's denser than oil.
See how only the red water
pours out?
Let's try some other
physical processes
that can be used
to separate mixtures.
Have any of you ever
squeezed juice from an orange,
or had fresh-squeezed
orange juice?
Ever noticed the pulp?
>> student: Ew, I hate pulp.
>> professor: Well,
if we squeeze the juice
from an orange,
we get residual pieces of the
orange's flesh in the juice.
Now, is the orange juice
with pulp a homogeneous
or a heterogeneous mixture?
>> student: It's a
heterogeneous mixture.
We can see the pieces
of the pulp.
>> professor: Right.
Some people like pulp.
However, we can use a strainer
to get the pieces out.
Watch.
We can even use filter paper
to separate the pulp.
The strainer and the filter
paper both have small holes
that let the liquid
drip through.
But the filter paper has holes
that are microscopically small.
>> host: We call the process
our teacher just demonstrated
"filtration."
Filtration is a physical
process used to separate
solids from liquids
by passing them
through a barrier.
The barrier, called a filter,
allows small particles
to pass through,
while larger particles
are blocked.
Filtration is used to separate
heterogeneous mixtures.
A porous barrier is used
to separate a solid
from a liquid.
Our porous barrier
is the strainer
and this filter paper.
Special filters can
even separate gasses.
Another way to separate water
and other liquids
is by using distillation.
Distillation is the process
that separates homogenous
mixtures based on
the different boiling points
of the substances.
It boils the liquid
from the other components,
and then a tube carries
the gas off to a place
where it can condense.
The mixture is heated
until the substance with
the lowest boiling point
boils to a vapor,
which can then be condensed
into a liquid and collected.
>> professor: Does anybody know
of anything that's distilled?
>> student: I actually use
distilled water to clean
my contact lenses.
>> student: Oil.
Like making gasoline.
I heard oil refineries
in Louisiana use distillation
to separate different
liquids from oil.
>> professor: That's true.
Good job.
Distilling gasoline from
crude oil is really hard to do.
So careful safety rules
have to be followed
when you're distilling oil
at a refinery.
Kerosene, gasoline, jet fuel,
and other substances
in crude oil boil
at different temperatures.
That's how a refinery
separates them.
Now, what would we do
if we want to separate
a pure solid from a solution
in which the substance
is dissolved?
For example, if we had
a big container of juice
from a sugar cane plant,
and I wanted to collect the
solid, pure sugar crystals?
>> student: If we boil
the juice, the water will boil
and the vapor will go
into the air, right?
>> professor: Right.
Boiling or evaporating
from a sugar or salt solution
will make the water
go into the air,
leaving solid crystals behind.
That's called crystallization,
which separates a pure
solid substance
from a solution containing
the dissolved substance.
>> host: We can see
crystallization
in evaporating seawater.
In this photo, you see what
happens near the Dead Sea,
in Israel, when water
evaporates from the seawater,
leaving salt crystals behind.
The seawater is
a homogenous mixture
with a high concentration
of salt dissolved in it.
So, during the day,
when the sun is shining bright,
evaporation takes place
where the water moves
from the liquid state
to being a gas.
In particular, near the shore,
this change of concentration
from the water being evaporated
causes the salt to recrystallize
and form salt pits
on the seashore.
If water from evaporation
is collected,
we can use that water
for human water supplies.
This purification process
is called desalination.
And this process certainly
produces very high quality
drinking water
in desert locations.
But desalination is a really
expensive way to purify water.
It can be difficult to separate
solids dissolved into liquids
on a large scale.
So let's get back
to our classroom
and learn about some
other separation methods.
>> professor: A different method
for separating dissolved
materials is called
chromatography.
In chromatography,
the parts of a mixture
are separated
based on the ability
of each dissolved component
to travel through materials
at different speeds.
Let's go back to our candies
to explore chromatography.
It'll be tempting,
but be sure not to
eat your equipment
before the experiment, okay?
You have a piece
of filter paper,
or a coffee filter.
Now, use a pencil to
trace a circle approximately
3 centimeters in diameter.
Now, write the numbers around
the edge of the filter paper
for each of the substances
to be tested.
In this chromatography
demonstration,
you'll use chemicals found
in candy and drink mixes.
You can also do this
with the ink from markers,
different types of pens,
or even leafy vegetables.
We'll see if chromatography
can separate the different
chemicals used to make
candy coloring.
Combine the drink mixture
with a few drops of water,
and then make a thick,
wet paste.
Now, add 1 drop of water
to each of the candies.
For each of the three
substances to be tested,
place a small dot
on the penciled line
by dipping a toothpick into
the colored liquid to be tested
and touching the paper.
Allow the spot to dry,
and re-spot it
in the same position.
Now, use a pencil to punch
a hole in the center
of the filter paper.
Now, insert a folded piece
of filter paper into the hole
as a wick.
Add water to these beakers.
Set the wick into the water,
with the filter paper
resting on top of the dish.
Water should move up the wick
and onto the coffee filter.
The chemicals that
dissolved in water
will move up with the water
onto the filter.
Large molecules won't
be able to move as far
as small molecules,
so mixtures will separate
in the paper.
Don't rush this.
It's a fun experiment.
I know you can handle it.
>> host: Now that our teacher
has given you the instructions
for setting up this experiment,
let's take a break,
and let you get to work
and record your own results
by drawing a picture
of your chromatogram.
Oh, I forgot to tell you.
A chromatogram is
a piece of paper on which
a solution has been separated.
That's what our teacher
just described.
And here's an important tip.
For accurate data, make sure
you remove the chromatogram
from the dish
before the water reaches
the edge of the filter paper.
Good luck with that,
and I'll see you at the top
of the next video for Unit 2.