In this video you're going to learn
how to use the technique of Suction Filtration.
When working with different chemicals,
solid precipitates can sometimes form in a liquid
called a supernatant.
In most cases, you'll only want one of the two,
either the liquid or the solid.
So being able to separate them is key.
The technique most common for this is Suction Filtration.
To do this, a partial vaccum is formed,
and special equipment is used.
This draws the liquid through the funnel into the flask
but leaves the solid behind.
Before you begin, it's important to make sure
that all of your filtration equipment is very clean.
You also need to make sure that
the glasswear doesn't have any damage.
If it's damaged at all, a crack, a scratch, anything,
it can cause fragile positions on the glass,
and when the vaccum begins it can cause
the entire glasswear to shatter.
Which can be very dangerous.
So make sure it's completely undamaged before you begin.
Once you have your thoroughly cleaned
and undamaged flask, you can attach it to a retort stand.
This helps to prevent it from toppling over later on.
You can use an adjustable clamp like I have or a ring clamp.
Make sure it's tightly fastened.
The type of filter you'll want to use depends
on the volume of the solution you'll need to filter.
I'll be using a Bčchner funnel but there's
also smaller ones which are referred to as Hirsch Funnels.
Make sure you choose the right size for the job.
You'll also want to make sure that your funnel
fits securely with a rubber stopper into the top of your flask.
The next step is to get a filter paper large enough
to cover all of the holes in the bottom of the funnel.
There's many different kinds of filter papers
so make sure you're using the right one for your application.
The last step is to moisten your filter paper
with a small amount of solvent.
Doing this helps it to adhere to the bottom of the funnel,
and prevents solids from leaking underneath the filter paper.
You'll now need to attach the aspirator to your funnel.
Each of the sinks in the lab will be set up with one of these,
there should be a hose coming out of
the side of the faucet as well as the bottom.
You begin by turning on the water,
you should be able to feel the suction
coming out the end of the hose.
Now gently attach this to the sidearm of your funnel.
Do this carefully because the side arm is delicate and can break.
You'll want to make sure that the hose draining down into the sink
is equipped with something to keep the hose from spraying out.
Such as a towel or a clamp.
Now that everything is set up, you can begin.
Start by double checking that your filter paper is secure,
and now you can begin pouring
your solution into the funnel.
It's best to do this by pouring down a stirring rod
to prevent splashing.
If your supernatants and your solids
are well separated like mine are,
do your best to keep them separated.
This will help the liquid to drain faster.
In some cases, you'll have large quantities
of supernatant, and it may overfill the funnel.
It's best to do this in small aliquots
rather than all at once.
If after you've drained the majority of your supernatant
you find that you have large quantities
of your solid remaining in the bottom,
the best way to handle it is to scrape it out
with the Rubber Policeman
on the bottom of your stirring rod.
Do this until all of your solids have made it's way into the funnel.
The objective is to separate the solid from the supernatant
as completely as possible. In some cases
this is very easy, but for some solids it may be helpful
to press down on the solids with
the end of your rubber spatula.
This helps to squeeze out the remaining liquid.
Be careful when you're doing this
so not to tear the filter paper.
Once all of your supernatant has been pulled through,
it's important to rinse your solids.
To do this you're going to use some cold solvent,
I've put mine in an ice bath.
First, remove the sidearm hose to stop the suction,
then pour a small amount of your cold solvent onto the solids.
Re-attach the sidearm hose to let the supernatant
filter out with the remaining solvent.
Repeat this 2 more times to thoroughly clean your solid.
When you've finished filtering, remove the hose
from the sidearm, and then turn the water off.
It's important to do this in this order,
because if you turn the water off first,
some of the water can wash back into the sidearm,
and into your flask, contaminating your supernatant.
If you were looking to collect your supernatant
it's now ready for further analysis.
But if you were looking to collect your solids,
you'll need to remove it from the funnel and filter paper.
To do this, remove the funnel from the top of the flask,
then scoop out as much of your solids as possible
onto a Watch Glass or into another receiving vessel.
You can do this by either using your Rubber Policeman,
or by using a Scoopula.
For large amount of solids, Rubber Stoppers work best,
but to get along the edges, use your Scoopula.
While doing this, you'll want to be careful
not to rip your filter paper.
You can remove the filter paper gently from the funnel,
scrape the remaining solids onto the Watch Glass.
Another good tip when doing this is to do it over a paper.
This is because if solids have spilled off of your Watch Glass,
you can recollect it without the benchtop contaminating it.
Using the Suction Filtration technique,
the solid and liquid components of your sample
can be successfully separated.