EXPERIMENT 4

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EXPERIMENT 4

• KINETICS An Iodine Clock Reaction

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Label a 150 mL beaker KI. Put 40 mL of KI in the
labeled beaker. Use this solution to rinse and
fill the 50 mL burette.
For making Solution A, place a 50 mL burette for
delivering KI in one side of the clamp and a 10
mL burette for delivering Na2S2O3 in the other
For making Solution B, place a 50 mL burette for
delivering the H2O2.
Label a 100 mL beaker Na2S2O3. Put 40 mL of
Na2S2O3 in the labeled beaker. Use this solution
to rinse and fill the 10 mL burette.
Label a 150 mL beaker H2O2. Put 60 mL of H2O2 in
the labeled beaker. Use this solution to rinse
and fill the 50 mL burette.
Set up two lab stands. Each of them with a
burette clamp.
Label one clamp KI and Na2S2O3, and the
other H2O2.
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Rinse each burette with a small portion of the
respective solution (3-4 mL). Make sure all the
inside walls, including the tip of the burette,
are rinsed!
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waste
Discard the rinsing solution into the 400 mL
beaker labeled waste.
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Fill each burette with the respective solution.
Make sure the tip of the burette is completely
filled, with no air bubbles.
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Label a 250 mL beaker H2SO4. Put 80 mL of H2SO4
into the beaker, and use a 10 mL graduated
cylinder for measuring this solution.
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Use another 10 mL graduate cylinder for measuring
the H2O. Use a full water bottle for filling the
graduate cylinder.
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To calibrate the dropping pipette so it delivers
1.0 mL, fill up the graduated cylinder with
water, then use the dropping pipette to withdraw
1.0 mL.
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Use a felt marker to mark the level of the water
on the pipette. This will be used to measure the
starch solution.
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Pour 20 mL of starch into a 50 mL beaker. Label
this beaker starch. Rinse the pipette with this
solution, and discard the rinsing solution into
the 400 mL beaker labeled waste.
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To obtain an accurate reading, you should be at
eye level with the meniscus (i.e. your line of
sight should be parallel with your reading).
To prepare Solution A1, add into a clean 150 mL
beaker, 5.0 mL of 1.0 M KI,
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5.0 mL of 0.0100 M Na2S2O3,
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10.0 mL of 0.75 M H2SO4,
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1.0 mL of starch,
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and 5.0 mL of distilled H2O.
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To prepare solution B1, add 2.5 mL of 0.025 M
H2O2. Check the bottle and record the real
concentration.
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Add distilled H2O to make the volume up to 24.0
mL.
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Add a magnetic spin bar to Solution A1, and start
stirring the solution.
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Add Solution B1 to Solution A1 and start the
stopwatch.
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When the solution turns blue, stop the stopwatch
and record the time.
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Record the temperature of Solution AB1.
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ATTENTION Do not pour the blue solutions down
the sink. Collect them in the 800 mL beaker. At
the end of the experiment empty the contents of
the beaker in the appropriate container in the
Acid Fumehood.
Prepare each of the other Solutions in Table I in
the same manner as Solutions A1 and B1.
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PART B Varying Temperatures/ Determination of
the Activation Energy (Ea)

• Choose one of the AB reaction solutions prepared
  before by selecting a reaction time that is
  midrange (neither too fast or too slow) at room
  temperature.
• You will prepare the selected AB solution 4
  different times and repeat the experiment at
  different temperatures, two above and two below
  room temperature.

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Put a magnetic stirrer in solution A.
Place both on a hot plate heating together until
they are at the chosen temperature (measure the
temperature of just one of them!). Do not exceed
50 oC.
Make both Solution A and Solution B (pour
solution B into a 150 mL beaker).
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Quickly place Solution A on the stir plate, start
mixing and pour Solution B into it. Start the
stopwatch and record the initial temperature.
Repeat the previous steps, heating to a different
above room temperature.
When the reaction is completed record the time
and final temperature.
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Place both in an ice bath cooling together until
they are at the chosen temperature (measure the
temperature of just one of them!).
Make both Solution A and Solution B (pour
solution B into a 150 mL beaker).
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Quickly place Solution A on the stir plate, start
mixing and pour Solution B into it. Start the
stopwatch and record the initial temperature.
Repeat the previous steps, cooling to a different
below room temperature.
When the reaction is completed record the time
and final temperature.