00:00:06
in this lab we will be studying a
00:00:08
chemical reaction at equilibrium between
00:00:10
two complex ion formations of
00:00:12
cobalt because they form complex ions
00:00:15
with water and or chloride ions very
00:00:18
favorably we can see which side of the
00:00:20
reaction is favored by the color changes
00:00:23
due to Crystal field Theory which is not
00:00:25
part of this um lab but we're going to
00:00:28
be studying later's PR ible and noticing
00:00:31
at equilibrium if a stress is made and
00:00:33
let's say a stress is made that forces
00:00:35
the reaction to go thermodynamically to
00:00:37
the right we should be able to see a
00:00:40
nice blue color because the reactants
00:00:43
get used up and will make more products
00:00:46
which will be of course that complex
00:00:48
with the chloride iion as chloride with
00:00:50
that ligan and of course back at
00:00:52
equilibrium if we do something that
00:00:55
favors the reverse um reaction where
00:00:58
we're going to make more
00:01:00
of the um Red by using up the reactants
00:01:04
and we will make more of the Cobalt
00:01:06
complex that has the water surrounding
00:01:09
it as the ligan which will be red we can
00:01:11
observe these shifts in equilibrium so
00:01:14
let's get
00:01:15
started so just to show you uh this is
00:01:18
the color or Baseline colors of the
00:01:20
Cobalt complex with water and this is
00:01:24
the color nice blue color of the Cobalt
00:01:26
complex uh with the chloride ion so
00:01:29
clearly you can see who's favored and by
00:01:32
looking at these colors and this is I
00:01:34
believe a purple color although I have
00:01:36
difficult time with colors of the
00:01:38
equilibrium mixture of both all right so
00:01:42
we're going to put out some test tubes
00:01:43
here and we're going to follow our
00:01:44
procedure as follows so here's our four
00:01:47
test
00:01:48
tubes and again right now we see the
00:01:51
pink color so all these test tubes
00:01:53
currently have a lot more of the
00:01:55
reactants and products as by the uh pink
00:01:58
color favoring the Copp complex with
00:02:01
water so we're going to Vin our first
00:02:04
test and we're going to just uh add some
00:02:06
hydrochloric acid into the first test
00:02:09
tube and doing so we see that
00:02:15
thermodynamically there is a shift from
00:02:18
this
00:02:19
reaction going to the side with the blue
00:02:24
compound so now we're making a lot more
00:02:26
cobalt chloride complex the complex that
00:02:28
is blue
00:02:30
okay and and very clearly you should be
00:02:33
able to figure out in your lab who is
00:02:36
being used up and who's being
00:02:41
[Music]
00:02:43
increased all right so in test tube two
00:02:46
we're going to add some calcium
00:02:49
chloride and we'll add some more and we
00:02:51
should be looking at the bottom of the
00:02:53
test
00:02:54
tube and the calcium chloride is going
00:02:56
to dissociate into its ion that's
00:02:58
important you understand into the
00:03:00
calcium plus two and the chloride
00:03:02
negative ions all right calcium is a
00:03:05
salt all right and as I probably bring
00:03:08
this closer to us we can see that the
00:03:11
bottom of the test tube show shows a
00:03:13
favored thermodynamic pathway meaning we
00:03:16
see a shift toward the blue side we are
00:03:19
making a lot more of that Cobalt ion
00:03:23
complex with the chloride
00:03:25
ion so clearly you are now shifting one
00:03:29
way now of course there's not enough
00:03:31
chloride ions to make full test tube go
00:03:32
but right where the salt is you can
00:03:34
clearly see there is some shift that
00:03:37
favors the formation of the blue complex
00:03:40
and you should be able to know which
00:03:41
side was shifting and in your lab or
00:03:44
which reactants and products are going
00:03:46
up or going down because of that all
00:03:49
right so that's one and two test now
00:03:52
we're going to grab test two number one
00:03:54
again and we're going to do another test
00:03:57
here
00:04:00
at some
00:04:04
point all right so here comes test tube
00:04:07
one again which we can see is clearly
00:04:09
favored all right with the blue compound
00:04:12
all right and uh now we're going to add
00:04:15
some
00:04:20
water all right so now adding some
00:04:23
Poland Spring water and again this is
00:04:24
not a uh uh they didn't pay us any money
00:04:27
to do this but we're going to add some
00:04:28
water and by adding water you can see
00:04:30
definitely a shift toward the pink uh
00:04:34
Cobalt complex and that pink Cobalt
00:04:37
complex um is on the reactant side so
00:04:41
again you should be able to figure out
00:04:42
where the reaction is Shifting to by uh
00:04:45
whether we making a pink or blue complex
00:04:47
here all right and again these colors
00:04:50
are due to Crystal field Theory where
00:04:52
we're drawing in the lians okay into the
00:04:55
D's orbitals and causing the D's to
00:04:58
split pretty cool stuff to go through so
00:05:00
test tube three here okay we're going to
00:05:02
add hydrochloric acid which we've done
00:05:04
already before and we're going to see a
00:05:06
shift um to that favors um the cobalt
00:05:10
chloride complex and you should know
00:05:13
what that shift does and now part of the
00:05:15
same test now is we're going to add some
00:05:17
silver
00:05:18
nitrate notice the silver nitrate bottle
00:05:21
when it comes into play here has a is a
00:05:24
um dark bottle that prevents uh light
00:05:27
from getting in too much cuz the silver
00:05:29
iron are affected by the Light any case
00:05:31
you see me adding some silver nitrate
00:05:35
and clearly I see some solid developing
00:05:38
as we like to call a precipitate and
00:05:40
that
00:05:41
precipitate is building up as I add more
00:05:44
silver nitrate and I also see a color
00:05:46
change here okay as I keep adding more
00:05:49
silver
00:05:51
nitrate I see it going from this blue
00:05:55
complex back to the pink side so I
00:05:59
definitely see a pink color developing
00:06:01
here as we add some silver nitrate so
00:06:05
probably going to bring this up to you
00:06:07
and see up close and personal what this
00:06:09
looks
00:06:11
like and there she is and you can see
00:06:15
the solid on the bottom the solid
00:06:16
definitely has a white color okay but
00:06:20
that's not what's affecting the color
00:06:21
this definitely went pink showing us a
00:06:24
definite shift in equilibrium to the um
00:06:28
Cobalt complex that has a pink color and
00:06:32
you should make the appropriate markings
00:06:34
in your
00:06:35
lamp something about making this
00:06:38
precipitate cause the shift to favor the
00:06:42
formation of the um reactants the
00:06:45
original reactants something to think
00:06:47
about there what did we do there that
00:06:50
caused that reaction to shift to the uh
00:06:54
side that produced the pink complex
00:06:57
silver nitrate H we should know about
00:07:00
the uh solubility PR uh rules of
00:07:02
solubility and what the silver ion must
00:07:04
have done okay so our final test now is
00:07:08
to put our test Tu 4 which is favoring
00:07:11
the pink side and I'm bringing a thermo
00:07:14
um an infrared thermometer to show you
00:07:16
that the um room or the board behind you
00:07:18
is 25.5 de C and the and the water I'm
00:07:23
bringing here is 76° C so I'm going to
00:07:26
use a hot bath and in this test we're
00:07:28
going to put the test tube four in the
00:07:30
hot bath and we're going to see what
00:07:32
kind of color change will happen now
00:07:35
we're changing the temperature here so
00:07:37
we're actually going to shift not so
00:07:38
much the equilibrium in truth we're
00:07:40
actually changing the equilibrium
00:07:42
position to favor one side or the other
00:07:44
by adding heat okay we are definitely
00:07:48
Shifting the equilibrium to a new
00:07:50
position that's favoring if you can see
00:07:53
the blue Co cobalt chloride complex all
00:07:57
right and that tells you something about
00:07:59
where
00:07:59
the heat is you know something about L
00:08:02
sher's principle you increase the
00:08:04
temperature the reaction is going to
00:08:05
shift to always do the opposite it's
00:08:07
response is opposite so looks like it's
00:08:10
shifting in response increasing the
00:08:13
temperature which means it's trying to
00:08:15
probably relieve that temperature and
00:08:17
this should tell you where the heat is
00:08:18
in this reaction okay is the heat go on
00:08:22
the reactant side or the product side
00:08:25
one of the questions in the lab okay is
00:08:27
to find out whether the board reaction
00:08:30
is endo and EXO and right here these
00:08:32
tests are telling you all right so in my
00:08:34
second test I'm going to add a cold
00:08:36
water bath and this test should also
00:08:38
support my understanding uh so here I
00:08:41
have my U infrared thermometer I get
00:08:43
about 9° of my ice bath here and I put
00:08:47
my my warm solution back into the ice
00:08:51
bath and we can probably guess what's
00:08:53
going to happen here and lowering the
00:08:55
temperature the reaction's going to
00:08:56
shift to do the opposite probably to to
00:08:59
um increase the temperature so it's
00:09:01
going to
00:09:02
favor
00:09:03
whatever shift of equilibrium that
00:09:07
favors um the increase in temperature or
00:09:10
the exothermic way you should know
00:09:12
decrease in the temperature is the
00:09:14
stress the reaction is going to changes
00:09:15
equilibrium to to do the opposite and
00:09:18
that hint of what's Happening Here
00:09:21
should tell you from the ice bath test
00:09:24
and the um hot bath test where the heat
00:09:27
goes in the reaction side is the forward
00:09:29
reaction EXO or is the forward reaction
00:09:33
Endo all right and we can clearly see
00:09:36
that the cold water bath made uh and
00:09:39
shifted the equilibrium to favor the red
00:09:43
complex all right and that's essentially
00:09:46
this lab from these uh tests independent
00:09:50
tests you should have be able to figure
00:09:52
out where the shifts have occurred and
00:09:54
who's increasing and decreasing and
00:09:55
definitely whether the forward reaction
00:09:57
is endo or EXO thermic all the players
00:10:01
involved are taking their bows here I
00:10:03
guess I left the water out hope this
00:10:05
helped
00:10:07
[Music]
