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 this video, we are going to focus on filtration and crystallisation.
Now the first thing that I need to point out is that physical
separation techniques such as these are used to separate mixtures only.
They cannot be used to separate the elements in a compound.
In later videos, we are going to look at how we separate the elements in compounds,
for example by chemical reactions such as reduction or by electrolysis
but in these videos, we are focusing on physical
separation techniques and how they are used to separate mixtures.
We are going to start by looking at one of the simplest separation techniques,
which is filtration.
Filtration is used to separate an insoluble solid from a liquid.
Now remember that the word insoluble means that a solid will not dissolve in a liquid.
So I have got here two chemicals.
On the left we have silver chloride and on the right we have water.
These small letters are called state symbols and they tell us the state of a chemical
for example whether it is a solid, a liquid, a gas or dissolved in water.
This little “s” tells us that silver chloride is a solid.
The little “l” here tells us that water is a liquid.
Silver chloride is actually insoluble in water, so it will not dissolve
and you would be given that information in the exam.
So I have a solid material suspended in a liquid and I am showing you that here.
Now obviously, this diagram is not to scale as you would not be able
to see individual particles of silver chloride, but you should get the idea.
Because the silver chloride is insoluble in water,
we can use filtration to separate these two substances.
To do this we use a filter funnel and a filter paper like this.
We start by pouring our mixture into the filter paper.
The liquid, in this case the water, simply passes through the tiny pores in the filter paper……
However, the solid material, in this case the
silver chloride cannot pass through the filter paper so it is trapped.
So in the end, we have got our liquid separated from our solid.
Filtration is a really useful separation technique and is used a lot in Chemistry.
Another important separation technique is called crystallisation so let us take a look at that now.
Crystallisation is used to separate a soluble solid from a liquid so
you can see that it is different from filtration.
In this example, we have sodium chloride and water.
Now the little aq here means that the sodium chloride is dissolved in water.
Scientists call this an aqueous solution.
We want to separate the sodium chloride from the water.
So here is our sodium chloride solution.
If we leave this solution for a few days, then the water will evaporate.
This will leave behind crystals of solid sodium chloride like this.
Now can you see that I have changed the state symbol for the sodium chloride from aq to s
Because now the sodium chloride is not dissolved in water, it is now a solid.
If we want to make crystallisation happen faster,
then we can gently heat our solution to evaporate the water.
However, we have to be careful that heating does
not affect the chemical that we are trying to crystallise.
For example, certain chemicals will break down if we heat them.
So sometimes it is better to just leave the water to evaporate on its own.
OK so hopefully now you should be able to describe
the physical separation techniques of filtration and crystallisation.