The Egyptian Nights Experiment
March 31, 2015
The purpose of this demonstration is to provide an eyecatching illustration of the
properties and behavior of reaction rates and kinetics in chemistry.
Note: This experiment is commonly referred to as both the Egyptian Nights Experiment
and the Iodine Clock Reaction. I prefer the former, and will use it exclusively moving
The idea for this demonstration comes from the British Science Association website
article titled “Get set… demonstrate” posted in 2013. The article explains the materials
and equipments required for the successful execution of the experiment, including
detailed instructions for the procedure. The URL for this source is included in the
sources section of this report. Please see the attached printout for the original procedure.
Present a background on the principle the demonstration illustrates. Explain the
chemistry behind the principle demonstrated, including equations where appropriate.
This particular reaction has become a classical demonstration used to display kinetic
chemistry in action. The experiment was originally developed by Swiss chemist Hans
Heinrich Landoldt in 1886. This type of reaction can be referred to as a chemical clock; a
mixture of reacting compounds in which the concentration of one compound displays an
abrupt change accompanied by a visible color appearing. In selfindicating reactions of
this type, in which nothing appears to happen for a period of time, and then a change
suddenly become visible, the onset of the color change may be used to time the reaction.
H2O2(aq) + 2I(aq) + 2H+(aq) ﬁ 2(aq) + 2H2O(l)
2S2O32(aq) + I2(aq) ﬁ 4O62(aq) + 2I(aq)
For the Egyptian Nights reaction the following materials are required:
0.2g soluble starch
4.1g sodium acetate
50g potassium iodide
9.4g sodium thiosulfate
30ml acetic acid
100ml hydrogen peroxide (30% concentration)
Distilled water, approximately 1.5L
Glass stirring rod
3 x 1L beakers
2 x 1L volumetric flasks
50ml and 100ml graduated cylinders
Throughout this demonstration it is important that protective glasses and gloves be worn
at all times. Sodium acetate, potassium iodide, sodium thiosulfate, hydrogen peroxide,
and acetic acid can cause skin and eye damage.
The soluble starch, sodium acetate, potassium iodide, and sodium thiosulfate must be
weighed carefully using plastic weighing boats, on the toploading balance. The boats
containing the chemicals must be labeled, as the reactants are extremely similar in
In a clean, dry 1L beaker, the soluble starch is mixed with the glass stirring rod into a thin
paste, using approximately 5ml of distilled water. When a homogenous consistency has
been achieved, the solution is diluted to 800ml.
Next, the sodium acetate, potassium iodide, and sodium thiosulfate are stirred into the
solution. It is important to stir the solution thoroughly, as the potassium iodide can be
chunky and slow to dissolve. Careful stirring will help achieve a transparent colorless
solution, which is key in achieving the shocking affect of this reaction.
This solution is now complete, and can be carefully poured into a clean, dry 1L
volumetric flask, labeled “solution A.”
The next solution requires 500ml of 6% hydrogen peroxide. As 30% hydrogen peroxide
is all that is available to the lab, a dilution must be made. In order to form 500ml of 6%
concentration, 100ml of 30% H2O2 is measured using a 100ml graduated cylinder, and
then diluted to 500ml with distilled water in a 1L beaker.
30ml of acetic acid is carefully measured using a 50ml graduated cylinder. The acetic
acid is added to the hydrogen peroxide solution, and is next diluted to 1L with distilled
water. This solution is now complete. It must be poured into the remaining volumetric
flask, and labeled “solution B.”
At this stage, the experimenter has 2 identicallooking solutions labeled A and B. The
solutions are clear and colorless – they look as though they could be water. It is time to
perform the demonstration now.
300ml of each solution is poured into the remaining 1L beaker together. This new
solution must be stirred vigorously for a few seconds with the stirring rod. After about 20
seconds, a dramatic color change will occur; the solution will change from transparent
and colorless to blueblack in an instant.
There is enough of each solution to perform the experiment several times. Additionally,
the timing of the color change can be manipulated by adding more hydrogen peroxide to
solution B, if desired.
When the experiment is complete, the resulting solutions can be disposed of down the
sink drain. The glassware is washed, dried, and put away.
It is interesting to observe that while the reactants used in this experiment are either
white, or colorless, the final result produces a spectacular color change.
Soluble starch appears as a fine white powder, it is dull and does not reflect light, similar
in appearance to flour used in baking. Sodium acetate and sodium thiosulfate are nearly
identical in appearance. They are both small white crystals, similar in appearance to table
salt. The only visible difference is that the sodium thiosulfate is a brighter, more vibrant
white color. The potassium iodide is also a white crystal, however, it appears in large
coarse chunks and must be chipped apart with an ice pick in order to isolate a small
portion for measuring.
The 30% hydrogen peroxide is translucent, odorless and colorless. It looks exactly like
water. The acetic acid is identical in appearance to the hydrogen peroxide, however, it
emits an eyeburning vinegary odor which is very intense and lingering.
In preparing solution A, the mixture required vigorous stirring for approximately 7
minutes in order to dissolve the potassium iodide completely. Initially the soluble starch
content led to a slightly milky appearance, but with vigorous stirring this dissipated
almost entirely, leaving just a trace of cloudiness detectable.
When mixing solution B, the addition of the acetic acid was similar in appearance to ink
being dropped into water. While both the acetic acid and the hydrogen peroxide solution
are colorless, a swirling effect can initially be detected.
Upon mixing solutions A and B in equal parts and stirring them together, a 20 second
period passes before the reaction occurs. This waiting time allows doubt and suspense to
build, making the change even more dramatic.
In videos of the experiment I’d viewed online, the reaction occurs within a fraction of a
second, changing from transparent and clear to completely black. During my practice run
in the lab, however, the reaction occurred over a period of several seconds. This was
disappointing to me; I decided it was an error in the dilution of the H2O2, which must be
done very carefully the day of the demonstration to achieve aswift color change.
Discuss any changes made to the procedure or chemicals as a result of your practice
runs. How do the changes make your demonstration more effective? Are there any
differences between your practice runs and your demonstration. Indicate how the
demonstration reinforced the principle it was meant to illustrate. Comment on the
success of the demonstration – whether it was visually effective, interesting to the
audience, appropriate to illustrate the principle it was meant to illustrate. Indicate any
problems with the demonstration.
Include any suggestions which might improve the demonstration.
British Science Association. Get Set, Demonstrate. 2013. [Internet article.] Cited
2, 2015. Available from: httpss://www.rsc.org/learn