[WATER BUBBLING] For experiment five, we get to do a really fun synthesis, which is the
synthesis of alum, which is really, really neat.
It crystallizes very well.
It has really big, beautiful crystals, and it's found in a lot of commercial crystal
growing kits.
You can see I'm, as usual, always wearing my safety glasses.
Even though I have regular eye glasses, I always have to wear my safety glasses over
those, and my protective gloves.
I am wearing nitrile, but you could also wear latex gloves.
And those are provided for you in the laboratory.
Today, we are working with sulfuric acid and hydroxide.
So we have to be especially careful.
If you ever experience a splash of any sort on your skin in chemistry lab, you need to
rinse it off right away.
Even if you're pretty sure it's water, there is that doubt there, so always rinse off right
away.
All right.
So the biggest skill that we're going to learn is a technique called vacuum filtration.
And this is really important.
It's one that you'll take with you to organic chemistry, so it's good to have a good foundation
now.
This looks like an Erlenmeyer flask, with a little outlet.
And this little arm makes it a filtration flask.
So it's hooked up with some tubing to an aspirator.
Once I turn this faucet on, the water will shoot down, and the motion of that water will
generate a vacuum, pulling through the top of this flask.
We have a Buchner funnel and a septum.
And this is going to fit on the top.
We have filter paper.
You can see from the holes in the top of the funnel, these holes are what allow the liquid
to flow through.
If you're using really big solids to filter, you might not need filter paper.
But almost all of what we generate is pretty fine or has some very fine or small particles.
So we use filter paper to allow the liquid or solvent to be pulled through, while separating
out the solid.
So I'm going to push that in a little bit with that rubber septum.
I'm going to turn on the aspirator.
And push it down a little bit with your palm.
And you can feel the suction as you're doing it.
If you can't feel any suction when you're doing that, check to make sure everything's
connected.
Another thing that is important to do is get your filter paper wet a little bit with whatever
solvent you're using to rinse your crystals.
In this case, I'm just using DI water as a demonstration, and you can see it pulling
through.
So these are just some solids that I'm using for the demonstration.
Your alum crystals will not look like us.
So I'm going to pour it a little bit slowly at first.
The reason I get my filter paper wet is because if it's dry and then you dump your sample
in there, a lot of times, it will just float to the top.
And we don't want that.
So you try to generate a bit of a slurry, so that your particles come out with your
solvent, scraping all of it out, because in this lab, you're going to do a percent yield,
so you want to make sure you get all of that out.
You can also use the solvent, which for this lab is some cold ethanol, to rinse out your
flask, to make sure you get all of the solid particles out.
And you can see it's pulling through.
If we didn't attach the aspirator, it would still filter, but it would take a really long
time.
So this makes it go a lot faster.
And I let it go for maybe 10 or 15 seconds even after all of the visible solvent has
been pulled through, just to help it dry a little bit.
Once that's done and you don't see any more liquid, you can break the seal.
You can either break it at the hose and then turn off the water.
And then, for this lab, you're going to take your filter paper and scrape off your product
into your beaker that you've already weighed.
We're not really worried about scraping or tearing up our filter paper, here, because
we're not going to use it again.
We just want to make sure we get all of that product.
You might want to let it dry a little bit before you transfer it into your beaker, to
make sure your mass is more accurate.
OK.
So then, we're going to weigh this.
What do we do with our filter paper, and what do we do with our alum crystals when we're
done?
Well, we're going to remove our filter paper.
And after we've recorded all of our data, you're going to walk over to the hood, and
you're going to find the solid chemical waste container.
And that's where you're going to put all of this material.
You're not going to throw it into the trash can.
You're going to put it in solid chemical waste.
So that's the technique that you're going to use for experiment five.