- [Instructor] What we have here is a molecular equation
describing the reaction of some sodium chloride
dissolved in water plus some silver nitrate,
also dissolved in the water.
They're going to react to form sodium nitrate,
still dissolved in water, plus solid silver chloride
and if you were to look at each of these compounds
in their crystalline or solid form before they're dissolved
in water, they each look like this.
But once you get dissolved in water, and that's what this
aqueous form tells us, it tells us that each of these
compounds are going to get dissolved in water,
they're no longer going to be in that crystalline form,
crystalline form.
Instead, you're going to have the individual ions
disassociating.
So for example, in the case of sodium chloride,
the sodium is going to disassociate in the water.
Sodium is a positive ion, or cation, and so it's going
to be attracted to the partially negative oxygen end.
Remember, water is a polar molecule.
That's what makes it such a good solvent.
Now, the chloride anions, similarly, are going to dissolve
in water 'cause they're going to be attracted
to the partially positive hydrogen ends of the water
molecules and the same thing is gonna be true
of the silver nitrate.
Silver ...
The silver ion, once it's disassociated, is going to be
positive and the nitrate is a negative.
It is an anion.
Now, in order to appreciate this and write an equation
that better conveys the disassociation of the ions,
we could instead write the equation like this.
This makes it a little bit clearer that look,
the sodium and the chloride aren't going to be necessarily
together anymore.
The sodium is going to dissolve in the water,
like we have here.
The chloride is gonna dissolve in the water.
The silver ions are going to dissolve in the water
and so are the nitrate ions.
So this makes it a little bit clearer and similarly
on this end with the sodium nitrate stays dissolved
so we can write it like this with the individual ions
disassociated.
But the silver chloride is in solid form.
You can think of it as precipitating out of the solution.
This is not ...
This does not have a high solubility, so it's not going to
get dissolved in the water and so we still have it
in solid form.
Now you might say, well which of these is better?
Well it just depends what you are trying to go for.
This form up here, which we see more typically,
this is just a standard molecular equation.
Molecular ...
Molecular equation.
It's in balanced form.
We always wanna have our equations balanced.
This right over here is known as a complete ionic equation.
The complete's there because we've put in all of the ions
and we're going to compare it to a net ionic equation
in a second.
Complete ionic equation, sometimes just known
as an ionic equation.
Now why is it called that?
Well, 'cause we're showing the individual ions
as they're disassociated in water.
Now, what would a net ionic equation be?
Well let's think about that a little bit.
Let me free up some space.
So one thing that you notice, on both sides of this complete
ionic equation, you have the same ions
that are disassociated in water.
So for example, on the left-hand side you have the sodium
that is dissolved in water and you also have
on the right-hand side sodium dissolved in the water.
It's not, if you think about the silver chloride being
the thing that's being produced, this thing is in ionic
form and dissolved form on both sides of this reaction
and so you can view it as a spectator, and that's actually
what it's called.
It's called a spectator ion.
Spectator ion.
If you wanna think of it in human terms,
it's kind of out there and watching the reaction happen.
Its value in this reaction is, well it was part of the
sodium chloride and its providing ...
So the sodium chloride is providing the chloride
that eventually forms the silver chloride,
but the sodium is just kind of watching.
Similarly, you have the nitrate.
The nitrate is dissolved on the left and the nitrate
is dissolved on the right.
So the nitrate is also a spectator ion.
So if you wanna go from a complete ionic equation
to a net ionic equation, which really deals with the things
that aren't spectators, well you just get rid of
the spectator ions.
You get rid of that.
You get rid of that, and then you see what is left over.
Well what we have leftover is we have some
dissolved chloride, and we write aqueous to show
that it is dissolved, plus some dissolved silver,
plus some dissolved silver.
Once again, to show that it's dissolved we write aqueous
and if you put those two together, you are going to get
some solid silver ...
Solid silver chloride.
And what's useful about this form, one it's more compact
and it's very clear what is actually reacting,
what is being used to build, and you can say hey,
however you get your chloride into the solution,
however you get your silver into the solution,
these are the things that are going to react to form
the solid.
Instead of using sodium chloride, maybe you use
potassium chloride and the potassium in that case
would be a spectator ion.
But either way your net ionic equation would be what
we have here.