So, let's kind of go back for
a minute, to this zinc hydroxide.
So we have zinc hydroxide as a solid, and
it's in equilibrium with zinc
two plus ions in solution.
Plus two O H minus ions in solution.
There's gonna be a KSP table or
a KSP value reported in the KSP table for
this particular equilibrium.
We can calculate how much
hydroxide is formed here.
We can also look at the KF table.
And zinc is one of those cations that
will form a complex ion with many,
many different ligands.
>> [COUGH].
>> One of the entries
in that table is you're
gonna find zinc two plus,
an aqueous solution,
plus four equivalents of NH three,
is going to be in equilibrium
with ZN NH three four two plus.
And we going to have a KF value for
this particular equilibrium.
Some of the times when you see these
equilibria written, there's like a really
large arrow going over to the right and
a very small one coming back to the left.
This is to indicate that most of these KF
values are very, very, very, very large.
They range sometimes from ten
to the eigth to ten to the 30th,
which means that this equilibrium is
going to lie heavily over to the right.
If we compared the solubility
of zinc hydroxide in aqueous solution
which has a very, very low KSP.
And we looked at what happens when
we put concentrated ammonia in here.
Just like we did in chapters 15 and 16,
where if we have a multi step process,
if we add those steps together,
we get one big giant equilibrium
expression that's gonna have a K value or
an equilibrium constant.
That's equal to the multiplied or
the product, in this case the KSP and
the KF, or
the product of the Ks of all the steps.
So what happens here is that zinc
ions are gonna be placed in solution,
and when those zinc ions
are placed in solution,
they're gonna Interact with ammonia.
A coordinate covalent bonds going
to form between these guys and
a complex ion is going to be formed.
What that does is that drops
the concentration of zinc two plus in this
solution and it's gonna shift this
equilibrium over here to the right.
If we have concentrated NH three,
or excess NH three present.
The zinc is gonna keep reacting
to form this complex ion and
it's gonna keep dissolving
this zinc hydroxide.
To set up the overall reaction for
this, is zinc two plus exist as
a product in the first reaction and
a reactant in the second reaction.
We can kind of for all intents and
purposes cancel those out.
This gives us an overall
equation of ZN O H two solid,
plus four equivalents of NH
three in aqueous solution.
This is gonna be in equilibrium
with our complex ion,
which is ZN NH three four two plus,
plus two Minus.
The K, or the equilibrium constant for
this is gonna be the KSP times the KF.
In each instance if KF is very,
very large,
then K is gonna be much
greater than the KSP.
And this is gonna tell
us that the equilibrium
is gonna shift over to
the right hand side.
And that, in this particular instance, our
zinc hydroxide solid will be more soluble.
In NH three than in water.
Now we don't have to go back and
get completely mad at Le Chatelier for
coming up with a principle that
doesn't work in certain circumstances.
It works perfectly.
This is proving that his point works very,
very well.
Because we have this particular solid,
it's gonna dissolve and
it's using applications of
Le Chatelier's principle to
describe the effect that's happening here.
I wanna leave you with
this comment when you
are mixing chemicals together in the lab.
Think of these pictorial
representations of what's going on.
And more importantly.
Think of the equilibrium established here.
And how that's gonna be affected when
you're adding your various reagents.
So don't just simply follow procedure.
Think about what's happening for
each of those steps.
