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Hi everybody, this video is going to discuss the procedures for completing
the clock reaction lab and
clarify some of the steps that are listed in the lab manual.
So as I mentioned in the previous video there are 3 parts to this lab, the first part
is to measure
initial rates of your target reaction
as a function of reactant concentrations so you're going to change
reactant concentration from one mixture to the next and for each one of them you're
going to measure initial rates.
For part two
you're going to measure the rate of the reaction,
with the same
set of reactant concentration
at different temperatures,
and for part three you're going to add a catalyst to the reaction and then observe
what the effect of that catalyst is.
Here is the list of all the reagents you're going to
need for this experiment.
They will be available in the hood, in
the fume hood
in the lab when you come in.
And so you can see that all the bottles listed on the right side are all the
reactants
and then you have
your catalyst which is this bottle right here, the small bottle
and the
yellow circle is the starch which is basically
it's not part of the reactants but it is used to identify the presence of
the product
iodine, in this case because the
color of the solution will turn blue once starch and iodine react.
This page lists all the different equipments that you're going to need in
addition to what you have in your locker.
So there will be a stopwatch provided
at the instructor's bench so you just need to pick one of them up. There are
two different versions here
and
it's fairly easy to use, one of the buttons is usually a start button and the other
one is the reset button
so first you want to reset it to zero and then you want to start
timing and you press that same
button to start as well as to stop okay.
For the one with 3 buttons, one of them is start
and I think the other one is reset and the last is for
editing the stopwatch or doing some kind of set up,
but they should be fairly self-explanatory, you can ask me questions
in the lab about them.
You're also going to need the hot water baths,
which I will
set up
previously for you
there are 4 water baths, they're located at
the north end of Science 301,
so you can take a look at them.
They should all be set up
at
various settings.
Two of them will be hotter,
two of these will be hotter, these guys would be at the lower temperature but still hot
okay
and one reaction is going to be done here and the other
reaction is going to be done in the hotter one.
And then you're also going to have an ice water bath that I will also set up near the
sink
for you to measure
the low temperature setting.
One thing t remind you, which is also mentioned in the lab manual is that you don't
want to watch glassware with soap because soap is going to interfere with
some the reactions so just make sure you rinse all your glasswares with deionized water.
So let's discuss part one. Remember here you just want to mix
various reactant concentration and measure the rate. The way
you're going to do this is you're going to
have 2 Erlenmeyer flasks as shown here,
in one flask you're going to put in
these three
reagents
water, KI and thiosulfate,
in the other
flask you're going to put in
bromate,
HCl and starch
and then you want to get
your partner
to have the stop watch ready to start
and then you want to pour
one of the flasks' content into the other one
mix it and at the same time start the stopwatch okay.
That's how are you going to
start the timing
and at some point once the clock reagent is consumed completely
iodine is going to be produced
and that iodine is going to react with the starch to produce a blue color.
This is an example of the color of iodine with starch
at different dilution factor
the one that you're going to
most likely see would be the one that is the deepest blue color here on the left, so
that is the color that you'll see.
You want to record or stop the timer as soon as you see blue
showing up,
so you want to make sure that your
Erlenmeyer flask is placed
on top of a white
surface so maybe a piece of white paper
so it's easier for you to see when the blue color shows up.
After you stop the timer, you also want to measure the temperature. The way you
measure the temperature is by
taking a thermometer and putting it into the reaction mixture
So for part two you're going to measure the rate of the reaction as a
function of different temperatures.
In this case, what you're going to do is you're going to
prepare
four
duplicates, you can do this all of the same time but most likely you're not going to have
enough glasswares so you're probably going to do them one-at-a-time but prepare
your mixture 1 from part A again
the same reactants you use for mixture 1 in part A,
into the two different flasks
before you mix them,
and what you're going to do is you're going to have four of these guys all set up at some
point
and basically the four
mixtures 1,
are going to be used to measure reaction at room temperature,
in an ice-water bath,
in a medium-heat bath,
and the high-heat bath, high temperature heat bath.
Now the lab manual
tells you that
you're going to measure the temperature at 3 degrees,
thirty degrees
and forty degrees. Now
the water baths that you're going to use don't have exactly this
setup.
You're just going to record the temperature that you actually see
on your thermometer so it might not be three degrees, it might be five degrees
but
you're still going to have
four different temperatures as the
temperatures you're going to use in order to get your activation energy.
So for the
medium- and high-heat water baths,
they will be set up in these water baths as I mentioned earlier in this video,
basically I'm going to set two of these as the medium-heat
and these last two to be the high-heat
water baths.
Now what you're going to do again is you see your reaction
flasks right here,
you're going to take both of them put them inside
the
water bath and let them
incubate.
For the medium-heat, you want to do it (incubate) for five minutes
before you mix
and for the high heat you want to do it for three minutes before
you mix.
And then once you let the two of them sit there for the
appropriate amount of time, either 5 or 3 minutes,
pour one into the other
mix it,
and just wait until the blue color shows up and then just
measure the time it takes for the product to show up,
and at the end, don't forget,
put a thermometer inside the flask,
and look at the actual temperature.
Like I said,
it's not going to be exactly thirty degrees or forty degrees, it's going to be a
different temperature
but you do have to look at that temperature and measure it
with your thermometer.
The ice water bath is the same thing
You're going to take your two flasks and put them in
an ice-water bath, which is basically just a container filled with ice,
Now you're gonna put that in
for
ten minutes,
so with the other water baths, I said it was
one for 5 minutes, the other for 3 minutes,
for the ice-water bath, make sure it's 10 minutes inside,
before mixing. So you're going to have two flasks in here,
the other flask is also in here,
and then once they've been in for 10 minutes, you'll mix one into the
other one, start the stopwatch and time it. When the blue color shows up you stop it
and then put your thermometer inside to measure the actual temperature of the
solution.
The last part is to add a catalyst which is a molybdate catalyst,
Mo,
and
that would be added into one of your two flasks,
then you're going to mix one into the other one and time it.
This is a fairly straightforward procedure so you can just read the procedure and follow through
and you should be able to make that observation.