Baku Higher Oil School
Petroleum Engineering Department
Process Industries A
Lab Report Number 2
The title of the experiment:
The Iodine Clock
Name and Surname: Rasul Alakbarov
Group Number: 22.1
Supervisor: Nargiz Khalilzade
1
Contents
Objective.................................................................................................................................. 3
Introduction ............................................................................................................................. 3
Theory ...................................................................................................................................... 4
Experimental technique ......................................................................................................... 6
Procedure ............................................................................................................................. 6
The required equipment:..................................................................................................... 6
Results ..................................................................................................................................... 8
Experiment 1. ....................................................................................................................... 8
Experiment 2. ....................................................................................................................... 8
Experiment 3. ....................................................................................................................... 8
Discussion part ..................................................................................................................... 10
Conclusion ............................................................................................................................ 11
References ............................................................................................................................ 12
2
Objective
The essential objective of this laboratory experiment named The Iodine Clock is to determine
how the rate of the reaction depends on the concentration of the reagents and the meaning of
the expression of the reaction rate.
The experiment consists of several stages and multiple reagents, including KI (Potassium
iodide), H2SO4 (Sulfuric acid), Na2SO3 (Sodium sulfate), H2O2 (Hydrogen peroxide), starch
and H2O (water). The reason why these substances should be used, is to determine iodine
ions during the experiment. It must be mentioned that, despite the fact that, we consume
different volume values of some reactants in each of 3 stages, the total volume of the mixture
at the end should be the same (0.05 L for our experiment) each time. Moreover, after adding
H2O2, the time that takes the mixture to change its color ought to be recorded precisely with
the aid of a timer, as this figure then will play an important role for our results. As soon as the
reaction finished by the color change to dark blue, the timer should be stopped in an instant
and the time value must be taken as a note. Then, we are able to figure out the rate of the
reaction easily with the help of collected data, as the rate of the reaction and the time is
inversely proportional. By using these data, we can also find the orders (m and n) of the
reaction, which after analyzing is found to be 333 and 333, orderly.
However, after comparing the calculated order values with given theoretical values, it can be
noticed that there are some errors which is quite normal in such laboratory experiments. The
possible causes of these errors and ways to prevent them will be mentioned in the discussion
part.
Introduction
Regarding to the iodine clock experiment’s history, firstly, the iodine clock was conducted and
explained in 1886, by Hans Heinrich Landolt, who was a Swiss chemist delved himself into
chemical kinematics. Consuming the data of the iodine clock experiment, we are able to
determine the equation of the rate of the reaction using the initial rate method. In addition, the
possible effects of concentration, pressure or humidity during the reaction, should be
considered. For example, if concentration couldn’t be ignored, the more molecules there are,
the greater the probability and amount of collisions; therefore, it is better to maintain normal
conditions while the reactions continue. Moreover, demonstrating the collision theory is one of
the primary purposes of this experiment. In details, the energy of the collisions between
substances should have a particular quantity of energy to break the bonds and build new
connections.
3
Theory
As mentioned in the introduction part, the purpose of this procedure is to determine iodine
ions in the solution, with the aid of color change to dark blue. Also, this experiment illustrates
the dependence of the rate of the reactions on the concentrations of the reactants. To begin,
the equation of the rate of the reaction is shown below:
𝑹𝒂𝒕𝒆 𝒐𝒇 𝒕𝒉𝒆 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏 = 𝐤 × [𝐀]𝒎 × [𝐁]𝒏
(Equation 1.)
In this equation, k - is the rate coefficient whose unit is mole/sec, m and n – indicate the order
of the reaction and they do not have units.
According to our experiment, [𝐀] and [𝐁] – represent the concentrations of H2O2 and I,
respectively:
𝑹𝒂𝒕𝒆 𝒐𝒇 𝒕𝒉𝒆 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏 = 𝐤 × [𝐇𝟐𝐎𝟐]𝒎 × [𝐈 − ]𝒏
(Equation 2.)
The predominant reaction of this experiment should be:
𝐇𝟐 𝐎𝟐 + 𝟐𝐇 + 𝐈 − → 𝟐𝐇𝟐 𝐎 + 𝐈𝟐
(Reaction 1.)
However, we start the experiment with the reaction between KI and H2SO4:
𝟐𝐍𝐚𝟐 𝐒𝐎𝟑 + 𝐈𝟐 → 𝟐𝐍𝐚𝐈 + 𝐍𝐚𝟐 𝐒𝟒 𝐎𝟔
(Reaction 2.)
For efficiency, it would be better to add reagents in this order to get higher profit:
1. KI 2. H2SO4 3. Na2SO3 4. H2O 5. Starch 6. H2O2
After we add Peroxide to the solution, a color change will be observed. Additionally, the time
interval from the addition of H2O2 to the solution to observation of precipitation, ought to be
recorded. It should be seen obviously that the color of the solution changes to dark blue,
which is related to the form of starch. Regarding to the second reaction, the same procedure
is again applied and the same period of time ought to be recorded precisely. In this kind of
reactions, the illustrated equation below can be used to figure out the rate of the reaction:
𝐑𝐚𝐭𝐞 𝐨𝐟 𝐭𝐡𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧~
𝟏
𝐭𝐢𝐦𝐞
(Equation 3.)
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To conclude, the laboratory work consists of 3 reactions, and, R_1 and R_2 represent rates of
the first and second reactions, respectively. Also, it must be mentioned that we should pay
attention to increase in the volume of H2O2 (0.02 L in first and 0.01 L in the second reaction).
Next, the consistency of reaction can be determined like this:
𝐑_𝟐 𝐭𝐢𝐦𝐞_𝟏
=
𝐑_𝟏 𝐭𝐢𝐦𝐞_𝟐
𝟐𝐦 =
𝒎 = 𝐥𝐨𝐠 𝟐
𝐑_𝟐
𝐑_𝟏
(Equation 4.)
(Equation 5.)
According to the first and third reaction, by applying the same way we are able to calculate n,
as we now the volume of potassium iodide increases from 0.01 L to 0.02 L:
𝟐𝐧 =
𝐑_𝟑 𝐭𝐢𝐦𝐞_𝟏
=
𝐑_𝟏 𝐭𝐢𝐦𝐞_𝟑
𝒏 = 𝐥𝐨𝐠 𝟐
𝐑_𝟑
𝐑_𝟏
(Equation 6.)
(Equation 7.)
As it was mentioned, there would be some errors at the end of the experiment, while
comparing the theoretical and calculated values and to we must figure out them by using the
equations below:
Absolute error = |𝟏 − 𝒎 or 𝒏 (𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒅)|
Relative error =
𝐚𝐛𝐬𝐨𝐥𝐮𝐭𝐞 𝐞𝐫𝐫𝐨𝐫
𝐭𝐡𝐞𝐨𝐫𝐞𝐭𝐢𝐜𝐚𝐥 𝐯𝐚𝐥𝐮𝐞
∗ 𝟏𝟎𝟎%
(Equation 8.)
(Equation 9.)
5
Experimental technique
Procedure
1) Before starting, each of the equipment and apparatus ought to be cleaned by utilizing
distilled water. As it was mentioned before, the order in which the reactants will be
added is crucial for our results (1.KI, 2.H2SO4, 3.Na2SO3, 4.H2O, 5.Starch, 6.H2O2).
1st experiment: KJ-0.1 L, H2SO4- 0.05 L, Na2SO3-0.05 L, H2O -0.2 L, H2O2 -0,1 L
2nd experiment: KJ-0.1 L, H2SO4- 0.05 L, Na2SO3-0.05 L, H2O -0.1 L, H2O2 -0,2 L
3rd experiment: KJ-0.2 L, H2SO4- 0.05 L, Na2SO3-0.05 L, H2O -0.1 L, H2O2 -0,1 L
2) After the ingredients are added to the flasks with the help of pipettes, we should
prepare water and starch to pour them to flasks. Despite the fact that the amount of
starch added to flasks stays unchanged during the experiment, the amount of H 2O2
changes regarding to the proportion.
3) Following this, the flask of hydrogen peroxide is added to the flask that contains the
remaining 5 ingredients and the flask must be shaken for about 3 seconds to make
solution homogenous. And at that time, the timer should be started instantaneously to
record the duration of the reaction, turned of at the time of color change to dark blue.
The recorded time should be taken as note. Also, with the color change, we can
observe the formed iodine particles in the solution, which means the experiment is
successful.
4) At the end of the experiment, the utilized apparatus ought to be cleaned with the aid of
distilled water and dried.
The required equipment:






4 burettes, size 50 ml (Picture 1.)
4 beakers, size 100 ml (Picture 2.)
Two pipettes, size 20 ml (Picture 3.)
4 funnels, (Picture 4.)
3 flasks (Picture 5.)
A stopwatch (Picture 6.)
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Picture 1. Burette
Picture 3. Pipette
Picture 5. Flask
Picture 2. Beaker
Picture 4. Funnel
Picture 6. Stopwatch
Results
7
Results
Experiment 1.
After adding the given amount of H2 O2 , we should start to record the time with the aid of a
stopwatch:
time_1=13.29 seconds (first attempt)
time_1=14.39 seconds (second attempt)
As this experiment has been conducted two times, we should use average time value:
t_1 (average) = (time_1(1st) + time_1(2nd))/2
t_1 (average) = (13.29+14.39)/2 = 13.84 seconds
Experiment 2.
Again, we should follow the same procedure to figure out the average time reaction takes
place:
time_2=7.26 seconds (first attempt)
time_2=8.06 seconds (second attempt)
t_2 (average) = (time_2(1st) + time_2(2nd))/2
t_2 (average) = (7.26+8.06)/2 = 7.66 seconds
Experiment 3.
In respect to the third experiment, the average time value ought to be found like this:
time_3=7.76 seconds (first attempt)
time_3=7.59 seconds (second attempt)
t_3 (average) = (time_3(1st) + time_3(2nd))/2
t_3 (average) = (7.76+7.59)/2 = 7.68 seconds
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And now, we are able to calculate the order m by using Equation 6. and Equation 7. :
2m =
𝑚 = log 2
13.84
7.66
13.84
= 0.853
7.66
Next, the same equations can be applied to determine n:
2n =
𝑛 = log 2
13.84
7.68
12.98
= 0.850
7.92
So now, the errors of each order should be calculated by using Equation 8. and Equation 9. :

For m:
Absolute error: |1-0.853|=0.147
Relative error:

0.147
1
∗ 100% = 14.7%
For n:
Absolute error: |1-0.850|=0.150
Relative error:
0.150
1
∗ 100% = 15%
Once the calculations have finished the final equation of the rate of the reaction must be like this:
𝑹𝒂𝒕𝒆 𝒐𝒇 𝒕𝒉𝒆 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏 = 𝐤 × [𝐇𝟐𝐎𝟐]𝟎.𝟖𝟓𝟑 × [𝐈 − ]𝟎.𝟖𝟓
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Discussion part
After completing all three experiments, we can determine the rate of the reaction. Moreover, it
should be noted that we determined the time intervals for each of the reactions with the help
of stopwatch described earlier. Additionally, all procedures have taken place in normal room
conditions, with a temperature of not below or above 20° Celsius. Regarding to calculations,
we must first consider that the rate of the reaction and time are inversely related. In fact, this
relation between them has already been revealed by scientists. In the first reaction, the
average time length of the reaction was 13.84 seconds and this figure went up to 7.66
seconds due to the increased amount of hydrogen peroxide. Because, according to the theory
of collision, the higher concentration, the more the number of collisions which causes the
reaction to end faster. If we look at the third experiment, the amount of potassium iodide has
increased twice, in comparison to the second experiment. However, the rate does not
change, which shows us that the precipitate separated until the previous reaction.
The errors of the experiment are illustrated below table:
Orders
m
n
Theoretical values
1
1
Determined values
0.853
0.850
Relative errors
14.7%
15%
Table 1.
However, there are some reasons of such errors and ways to alleviate them:
1. Timing inaccuracy is considered to be the most common
cause. As the stopwatch is started and turned off by a
human, human factor can result in inaccuracy during the
recording of time. Because, not all people have the same
reflexes and when they notice iodine particles in the
mixture, each of them can need different length of time to
stop the stopwatch, which leads to errors on the
durations of experiments. To alleviate this factor to some extent, the experiment should
be conducted several times and the average of measured time values ought to be
considered as the length of the experiment. As the noted figures will be more and less
than theoretical time figure, the average of them can be close to theoretical time value.
2. Moreover, it is possible that because of dark blue color, the
iodine ions can be noticed late by the specialist, as it is hard
to see these small particles in dark solution. So that, the
measured time can be longer than the theoretical time value.
To prevent this, we can use a brighter room, which allows to
determine ions in solution more easily.
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3. The other reason for errors is defective equipment utilized in experiment. To cite an
example, with a pipette that has a defective scale, it is impossible to accurately add
any substance to the solution, and this necessarily leads to incorrect measurements. In
addition, sometimes observers do not look perpendicularly at measurement glasses
such as burettes, pipettes, and beakers. This phenomenon is called parallax in
science. To prevent these factors, more proper apparatus should be used and during
the measurement the observer has to look the equipment perpendicularly.
Conclusion
To conclude, the rate of the reaction has been determined with the aid of 3 reactions. We
utilized a stopwatch to record the time from the addition of hydrogen peroxide to the
precipitation of iodide. As we got required time values of each reactions, the orders m (0.853)
and n (0.85) could be calculated to find the rate expression. However, when we compared
calculated values with the given theoretical ones, some errors were noticed. Discussion part
shed light on errors’ feasible causes such as defective equipment, “parallax” event, dark color
of the solution, human factors and lightless room. To alleviate and prevent these causes, we
can use proper apparatus in labs, during measurement look the equipment perpendicularly,
conduct the experiment several times and get the average time value, and utilize a room that
has good lightning system. As a result, the experiment has been conducted successfully.
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References
I.
II.
III.
IV.
V.
Chemical Engineering Laboratory Manual
RSC Education
Universty of Washington, Iodine clock reaction
Bellevue College, Reaction Kinetics: The Iodine Clock Reaction
Iodine Clock Practical Preparation (Teresa Kutsoati and Marian Kutsoati)
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