Hi. It's Mr. Andersen and this is chemistry essentials video 2. It's on chemical
analysis. One of the first early chemists, Jons Jacob Berzelius, who was Swedish, came
up with a way that we write out chemical formulas. And I love this picture here. It's one of
those where no matter where I move, he seems to be watching me. But, so when we write out
CH2O, which is actually going to be the empirical formula or the simplest formula of a sugar,
let's say glucose, we owe it to him for that. But if we look at the actual structure, this
is what glucose looks like. So it's going to have 6 carbon, 12 hydrogen and 6 oxygen.
But chemical analysis is simply looking at a compound, like glucose for example, figuring
out what's in there, how much of that what and then how it's all connected together.
And so in chemical analysis we're looking at compounds. And remember compounds are going
to be made up of atoms. And each of those atoms have a specific mass. And so what we
can do is look at the percent mass. In other words how much of that mass of that compound
is made up by each of those different atoms. That tells us what the composition is. It
also can help us figure out the empirical formula. That's that simplest chemical formula.
And it also can be used to test the purity of a substance. In other words is it just
that or are there other things that are added inside there. And so let me give you an example.
And we'll come back to this at the end of the video. Let say we take vitamin C and we
put it in a mass spectrometer, which is going to tell us the percent mass of all of the
atoms that are found inside it. And then we get this spit out. So we've got carbon, hydrogen
and oxygen. And it tells us the percent mass of each. In other words it tells us how many
grams are going to be made up of each. Could we figure out the empirical formula? Well,
we will. We're going to get back to that in just a second. And so let me use analogy to
begin with. So just like matter is made up of atoms, we could talk about something like
a big Lego structure being made up of Legos. And so let's say we had this base unit and
it weighed 2.5 grams. It doesn't matter if we have a larger or even a larger unit made
up of those smaller blocks. It's all going to have the same average mass. In other words
is we divide by the number of bricks, we're still going to have an average mass. No matter
how big the sample of those Legos is. But now let's get to solving it the other way.
In other words if I give you a big structure that weighed 320 grams, could you work backwards
to figure out how many bricks are in that structure? Well you would use factor-label
to figure that out. In other words, if each brick weighs 2.50 grams I can write it out
like this. Now we can cancel off those grams. And so what I get is 128 bricks in that structure.
And so what we can do is we can work backwards from that mass and we can figure how much
stuff is inside there. Now when we're working with chemistry we don't deal with bricks.
What we're going to work with is something called a mole. And so let me use gold as an
example. Let's say I had 1 mole of gold. Or 4 or 32. It's all going to be the same mass.
And what is a mole? I'll talk more about that in the next video. It's essentially a usable
amount of an element. A usable amount of a compound. And so all of these are going to
have the same average mass. 197 grams per mol. Now where am I getting that 197? Just
like 1 Lego piece weighs about 2.50 grams, 1 mole is going to weigh around 197 grams.
And so where do we find that? On the periodic table. And you should get used to just opening
up that periodic table. And so if we look at gold, its atomic mass number is going
to 100, around 197. In other words it's 197 atomic mass units or if we have one mole of
it, it's going to be 197 grams. So it's going to have the same average mass. And so what
we can do is we can convert to moles. We can, just like we converted to bricks we can convert
to moles. And let's say I have 2 ounce chunk of gold, which is around 56.7 grams. And so
what I could do is since I know that 1 mole is going to be 197 grams, I could cancel off
those grams again. What I could come up with is about 0.288 mole. And so a mole is going
to tell us how much of that element is going to be found. So let's go back to that problem
again. Let's say we're given some vitamin C. We put it in a mass spec and we get this
data out of it. What is that telling us? It's telling us the percent of each of those inside
there. And so what we could do, let's throw that data out here, is we can convert it to
moles. And once we have it in moles, we could figure out the empirical formula. So just
like we did with the gold, how do we convert this to moles? Well we'd have to get out the
periodic table. And so since carbon has an atomic mass of 12.01, we could write out this
conversion. We're going to cancel off the grams of carbon and would be 5.11 moles of
carbon. Likewise if we were to convert the hydrogen, again it's going to have a different
atomic mass number. We could convert those grams of hydrogen. And it would be 6.80 moles.
So that doesn't tell us much yet. Let's go to oxygen. Oxygen's atomic mass remember is
16. So I could cancel this off. And now we get 5.11 moles. Well that's weird that these
are the exact same. Not really. It's just our first piece of evidence that there's the
same amount of carbon as there is oxygen. Let's simplify that a little bit. So since
we divide them each by 5.11, we get one of the carbon to 1 of the oxygen to 1.33 of the
hydrogen. Now should we write it out like that? You've never seen a chemical formula
written with anything aside from whole numbers down here. And so what we could do is multiple
the whole thing times three and now we get the empirical formula of vitamin C. Or ascorbic
acid. Now is that really what it looks like? No. And we'll get to that later. This is what
it looks like. So it's actually going to have 6 carbons. It's going to have 8 hydrogens.
And it's going to have 6 oxygens. But you can see how we can use the mass to figure
out what's in there. And then how much of that what is going to be found in there as
well. We could also use a mass spec to figure out the purity. So if we were to throw that
vitamin C in there and we get kind of evidence like this. Well that tells us there's a lot
of carbon, hydrogen and oxygen. But we also have some impurities in there. We have some
mercury and palladium which is something that you don't want in your vitamins as well. So
could you fill out this concept map? Could you fill out the spaces? Could you pause the
video right here. Okay let's go through it. Chemical analysis is used on compounds, which
are made of atoms. Which each of those atoms have a specific mass. Remember we can therefore
use the mass percent to figure out the composition. In other words what is in the compound. We
could use that to figure out the empirical formula which is the simplest whole number
formula. And then we could also use that to figure out the purity of that substance. And
so did you learn the following? This is what I was hoping you would learn. Number one,
you could use mass data to identify or infer the composition of pure substances and/or
mixtures. So again we just look at the mass percent of everything that's inside there.
And then the second thing. Could you use mass data in order to justify a claim regarding
the identity or estimated purity of a substance? And so those are the two things that you should
be able to do. We learned how to figure out the empirical formula. And I hope that was
helpful.