Hi. It's Mr. Andersen and this is chemistry essentials video 27. It's on molecular, ionic and net
ionic equations. And so in chemistry you should be able to observe something. So let's say
watching of a bunsen burner. Figure out what are the chemicals that are combining in that
reaction. Write out a balanced chemical equation. And then depending on what kind of a reaction
we're looking at, you may want to use a different type of equation. And so let's start with
the combustion of methane. And so what comes out of a bunsen burner is going to be methane
gas. It's CH4. So one carbon and 4 hydrogen atoms. It's going to combine with oxygen,
which is going to be 2 oxygen atoms in an oxygen molecule. And then we're going to get
combustion. And so what is yielded in that reaction? We're going to make carbon dioxide
and water. And so that's what this arrow stands for. Now if you look at this, the thing that
should jump out right away is I don't have enough hydrogens on the right side compared
to how many I have on the left side. And so what I could do is I could add another water
on the right side. I'm trying to balance it. Now when I look at it, well, I'm good on the
hydrogens on either side. But now I've got too many oxygens on the right side. So I could
add another oxygen molecule on the left side. Now we have a balanced chemical equation.
We're just looking at the particulates here. What does this mean? In combustion of methane,
1 mole of methane is going to combine with 2 moles of oxygen to make 1 mole of carbon
dioxide and 2 moles of water. We have a balanced equation. And so in chemistry you should be
able to go from observing something, kind of writing out the particulates. Going to
an equation. And then starting to utilize that. And so when you have chemical change,
remember what's happening is we're breaking bonds and forming new bonds. What we can do
is we can write a chemical equation that represents that. It has to be balanced in order for it
to be useful. Especially when we're looking at stoichiometry. And so a general equation
of that is going to be a molecular equation. That's the kind of chemical equation you've
used your whole life. But there are two other equations that are important. One is an ionic
and sometimes we call it a complete ionic equation. This is most important when we're
looking at ions dissolved in solution or in aqueous reactions. And then there's something
called a net ionic reaction. What that allows us to do is really just look at the atoms
that are important in that equation. And that will also become important when we're looking
at redox reaction. But all of these equations we should be able to go back to that particulate
and really understand what's going on in a chemical reaction. And remember chemistry
is a laboratory science. And so you should be able to observe something in the laboratory
and then come up with one of these equations for it. Now a great way to look at balancing
equations is on phet. And so what you can do is you can go there and you can actually
set up balanced scales of the atoms. So here we're looking at making ammonia. I can add
1 of each of these. 1 mole of each of these. And I can see that it's not balanced. On the
left side I have too many nitrogen. Now I can balance it with hydrogen. And you can
see I get a smiley face because I've balanced the atoms on either side. And so remember
you can't change the molecule. But you can change the coefficient in front to balance
it. Now we've got water. So I didn't have enough oxygen on the left. And now I balanced
it with hydrogen on the right side. Or if we're looking at combusting methane. I add
1 of each. And then I find that I don't have enough hydrogen on the left side. So I can
balance that, or on the right side. And then I can balance my oxygen out. What's fun about
this is once you think you've got it, you can go to a balancing game where it will serve
really different equations at you. Some are going to be really easy. Some are going to
be hard. And then you balance it. And when you think you got it right, then you can check
it. And then if you're right it will give you the smiley face and you can go on to the
next one. And it's going to time you. And so it's a lot of fun. So balancing equations
is important. And it's a step that you always want to do when you're looking at any equation.
And so let's go back to this bunsen burner again. So the first thing you're going to
do is observe it. Next thing you're going to do is try to describe what happens. So
methane is combusting in the presence of oxygen to create carbon dioxide and water
vapor. We then write the reactants and the products. And that arrow stands for yields.
Next thing we do is we balance it. So we can write coefficients in the front to make sure
we have the right amount of atoms on either side. And then the one thing that we should
also include on a nice equation is what state it's in. And so in the reaction we have gases
combining to create carbon dioxide gas and water vapor. And so now we've got a molecular
equation. And now we can use it to do stoichiometry for example. And to make measurements. But
now let's go to an aqueous reaction. And so in this reaction we're taking lead nitrate,
which is clear. And we're adding it to a solution of potassium iodide. And it produces a yellow
precipitate. And so what we're getting is a solid that comes out of that. And so I could
observe that. I could know what those chemicals are. And then I'm going to write it out. So
we've got a solution of lead nitrate. A solution of potassium iodide and it's making a yellow
precipitate of lead iodide that settles to the bottom. Next thing I want to do is I want
to write out my reactants and products. Now if you don't know who to write, go from the
name of a chemical to it's equation, and vice versa, I'll put a link down here to a naming
molecules or naming compounds video that should help out. So the first thing I want to do
is I want to write out all the reactants and products. So now we've got lead nitrate, potassium
iodide making lead iodide and potassium nitrate. Next thing I want to do is I want to make
sure that I balance it. And so I can see right here that I don't have enough iodine on the
left side. So I could add a 2 there. Now I've got too many nitrates on the left side. So
now I could balance it like that. I also have to write the state that it's in. So I remember
those first two were aqueous. But this lead iodide is a going to be a solid. And now I've
got a nice molecular equation. But again this video is about two other equations. We've
got ionic equations and then net ionic. And so how does that work? What is an ionic equation?
Well if you think about this lead nitrate right up here, it's not sitting in that solution
as a connected molecule. Remember it's going to break apart into its ions. It's going to
have its lead ions and nitrate ions. And those are going to disassociate from one another.
Those are going to separate from one another. And so when I'm writing out an ionic equation
what I have to do is I have to write out all of the ions. And so let's do that one first.
I'm going to have that lead ion, which has a 2 plus charge. And then 2 of those nitrates
which have a 1 minus charge. Now why am I writing a 2 here? Because we have 2 of those
nitrates. And so you can see in an ionic equation what I'm doing is I'm busting apart each of
those ions. Let's go to the next one. So that potassium iodide, I'm going to break that
apart to its two ions as well. You can see that I'm writing that this is in solution.
So it's aqueous. Next we get to the lead iodide. Now remember that lead iodide is a solid.
It's that yellow solid, and so I'm not going to bust that apart into its ions. I'm just
going to write that lead iodide as a solid. But then this potassium nitrate is going to
break apart into its different ions. So I'm going to write it out like that. So I know
that's a lot of work. But this is a complete ionic equation. Why is that important? It
really allows us to look at what ions are in that reaction. And so if it's ever an aqueous
reaction, lots of times we'll use this ionic equation. Sometimes they'll call it a complete
ionic equation because it's showing all of the ions that we have present. Okay. What's
the third type of equation? That's going to be the net ionic equation. So if we look back
at this equation you can see that we have 2 nitrate ions on the left side. And we also
have 2 nitrate ions on the right side. And so they're really not being changed in this
reaction. And so we call those spectator ions. They're really just watching. And so what
you can do is you can cross out things on the left side that are also found on the right
side. As long as they're in the exact same form. Can you find something else on the left
side that's also on the right side? That's going to be those potassium ions. So I could
cross those out as well. And so once I've crossed out all those spectator ions I can
write it out like this. And that's going to be my net ionic equation. So that's, really
it's just showing what atoms are part of this chemical reaction that are actually forming
these bonds. And this will become important when we're looking at redox reactions in the
front. So now once you've got those equations, so this would be a molecular equation, then
you should kind of be able to work back to those particulates. And so let's write out
the ionic equation just using symbols. Using those diagrams rather. Using those molecules.
And so we have lead and nitrate ions. This is what they're going to look like in solution.
Remember they're not connected. They're dissolved in the water. Next we're going to have the
potassium and the iodine. So those are going to be separated as well. This is going to
be the iodine, or the big purple spheres. And the small purple spheres are going to
be the potassium. And now we're going to have a reaction. And what does it look like after
that? Then we're going to have the nitrate and the potassium ions. Again those are spectator.
They didn't change. Then we've got the lead iodide. You could see that's that yellow solid.
And so this is really what we're representing in an ionic equation. And then in an net ionic
equation what it's showing us is that we just have those lead and iodine ions that are combing
together to form that lead iodide. And so that's going to be a real simple form of that.
So did you learn to translate an observed chemical change into a balanced equation of
the correct type? Remember there are three types. Molecular is the one you're familiar
with. Ionic is when we're breaking it apart to show all the different ions. Net ionic
however is when we're just showing the atoms that are part of that chemical reaction. And
I hope that was helpful.