- [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. 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.