Welcome back to freesciencelessons.co.uk. By the end of this four part video, you should be
able to describe physical separation techniques. These include filtration, crystallisation,
distillation and chromatography. In the last video, we looked at
filtration and we looked at crystallisation. In this video, we are going to look
at distillation so let us get started. When we looked at crystallisation,
we saw that we can evaporate a liquid such as water from a solid,
leaving us with crystals just like this. The problem is, what do we do
if we want to keep the liquid? In this case we use distillation. So distillation can be used to separate a liquid
from a solid if we want to keep the liquid. Now I should point that we call this simple distillation. There is another technique called fractional distillation and this allows us to
separate two different liquids. We are going to look at fractional
distillation in the next video. So how does simple distillation work? There are two stages to this process. First we evaporate the liquid by heating. We then condense the vapour back
to a liquid by cooling. Let us look at the apparatus that we use to do this. We place our solution with the liquid
and dissolved solid in this flask here. This flask is now connected to a continuous glass tube which I am showing you
with this yellow arrow here. The glass tube is surrounded by a
jacket which we call the condenser. Cold water from the tap continuously runs
through the condenser and by doing this, it keeps the internal glass tube cold. After running through the condenser,
the water simply goes down the sink. We have also got a thermometer
as part of the apparatus here. So let us how see how this works. We start by heating our solution for
example by using a Bunsen burner. As we heat the liquid, it starts to
evaporate, turning into a vapour. This vapour now rises up the glass tube like this. The thermometer shows us that
the temperature is rising. Actually with simple distillation,
we usually just boil the liquid. The vapour now passes into the condenser. Remember that the condenser is kept cold
because we are circulating cold water around it. This means that the vapour now condenses, turning back into a liquid as it pass
through the condenser, like this. We can collect the liquid in our beaker. At the end, we are left with crystals
of our solid in the flask here ... and our liquid is in the beaker here. So that is simple distillation. Simple distillation can be used to
produce drinking water from sea water. However, a great deal of energy is
required for simple distillation so generally it is not used
to make drinking water. Other techniques are used instead. OK so hopefully now you can describe
how simple distillation can be used to separate a liquid from a solid
if we want to keep the liquid.