Hi. It's Mr. Andersen and this is chemistry essentials video 3. It's on the
mole. The mole is an incredibly important term. But remember it's just a number. It's
Avogadro's number. Why is it important? Well it allows us to deal with the massive number
of atoms that are found in matter. This is one of my favorite demonstrations. You take
a five gallon jug. Put a little bit of alcohol in it, like ethanol. And when you light it
you get this huge Whoosh, and this huge combustion of the ethanol. If we were to write out the
formula, it looks like this. Why am I talking about this when I'm talking with moles? Well
remember those coefficients that you write in front of the compounds in an equation like
this represent the number of moles. In other words how many massive number of atoms are
interacting. So it's really important when we deal with chemistry to understand what
the mole is. And the mole is simply Avogadro's number. It's a number. It's 6.02 times 10
to the 23rd. Where does that number come from? It's derived from the number of atoms in 12
grams of carbon 12. But it just gives us a usable amount of material that we can work
with in the lab. So if we're ever looking at a reaction like this the coefficients remember
are going to represent the moles. But it also serves as a bridge most importantly. A bridge
between the mass of an object and the number of particles that are found within that object.
And so where does the name come from? Avogadro was a Italian chemist. Worked many years ago
in the early 1800s. And so he came up with Avogadro's law. Basically as we increase the
volume of a gas, he proposed that we were increasing directly the number of particles
that are found within that. It didn't matter what the gas was. Now he died before they
actually came up and quantified this idea of the mole. But we still give him credit
for that early work. And so 1 mole is 6.02 x 10^23. But it's just a quantity. It's like
if I have one egg we call that an egg. But if I have 12 eggs we call that a dozen. And
so a mole is just a number. We could have a mole of anything. But it's most important
when we're dealing with chemicals. To give you an idea of how massive this number is,
imagine if I had a mole of marbles. So just regular marbles like this. And I were to start
covering the earth. Well I could cover the earth in marbles and that covering of the
earth would be 3 miles thick. And so there's a huge amount of numbers in Avogadro's number.
And so when you're dealing with even small amounts of a compound, small amounts of an
element, you have to understand that you have that many atoms that are found within there.
Massive amounts. Again it forms a bridge. It forms a bridge between the mass of an object
and the number of particles that are found there. And so it's really important at that
kind of a bridge point. And so let's talk briefly about what an atomic mass unit is.
And so let's say we take carbon dioxide for example. It's going to be found in the air.
You breathe it out. It's atomic mass unit is going to be the mass of each of the individual
atoms. And so we have 1 carbon. So we could look on the periodic table. And the atomic
mass of that is 12.01. And then we're going to add 2 oxygens. Each of those are 16 on
the periodic table. We could find it here. And so its atomic mass unit of carbon dioxide
is going to be 44.01. And so what is an atomic mass unit? It's the mass of one nucleon. So that
could be the mass of a proton or a neutron. Now why is that important? 1 mole of carbon
dioxide then is going to way 44.01 grams. Let's say we're looking at nitrous oxide. Could
you figure out the atomic mass unit of that? You could pause the video and try to figure
this out. Well you'd have to find the nitrogen. You'd have to find the oxygen. And we'd simply
add that up. So it would be 30.01. But if we had a mole of nitrous oxide that would
be 30.01 grams. And so it forms this bridge between the mass of an object and then the
number of particles that are found within that. And this is where sometimes people get
confused about the mole when they're trying to make these mole conversions. And so let's
say I had 9.01grams of water. It's almost 10 milliliters of water. And so that would
be about 2 teaspoonfuls of water. And let's say I wanted to figure out how many molecules
of water are found inside there. Let me show you how the mole can act as a bridge. So we
have 9.01 grams of water. The mole is going to act to convert that into the number of
particles. So first we use this mole conversion. Remember 1 mole of anything is going to be
the atomic mass of that in grams of water. So where am I getting the 18.02. I'm adding
the 1 oxygen, 16 plus the 2 hydrogens. And so one mole of water is going to be 18.02
grams. And so what I could do is I can cancel those grams. So now I've converted it to moles
of water. Now we use Avogadro's number. And so I'm going to take 1 mole of water is equal
to a number of molecules of water. So 1 mole is equal to Avogadro's number of that. I can
now cross off my moles. And now I can solve for the number of molecules of water. And
what I get, the math is easy here since I'm taking this, dividing by 18.02, we get 3.01x10^23.
And so I mean wrap your head around that for just a second. 2 teaspoonfuls of water,
the number of water molecules that are found in there would cover the earth in marbles,
if we converted those molecules to marbles 1.5 miles thick. And so now let me give you
one for you. Let's say we have 5.72 grams of glucose, C6H12O6, could you convert that
to molecules of glucose? And so here are the atomic masses here. I'll put the answer in
the video description down below so you can check and make sure you're doing it right.
Remember that mole serves that bridge. It's also incredibly important in chemical reactions.
This is one of my favorite reactions. This is a thermite reaction. We're getting a combination
of iron oxide with aluminum. And so since it has the oxygen source inside it, this would
burn under water if you want it to. Okay. So what did we learn in summary? Could you
pause the video and fill out what's in the blanks? Let me do that for you. So a mole
is Avogadro's number. Do you remember what that is? It's going to be 6.02 times 10 to
the 23rd. It's going to form a bridge between mass and the number of particles. And then
we use it to quantify chemical reactions. And so when we're looking at those coefficients
in the front of any kind of chemical reaction, it's going to tell us the number of moles.
And so what should you have learned? Did you learn this? That the mole allows us to connect
particles, moles, mass, volumes all together. Both qualitatively in the form of for example
a chemical reaction where we're writing that out. And quantitatively. Actually calculating
the number of particles in material. So that's the mole. It's just a number. And I hope that
was helpful.