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ARTICLE
The Canadian Science Fair Journal
CSFJ | Vol. 1 | Issue 1
© Suuronen 2018
the seawater reacted with the calcium carbonate of the shell,
Reac-
tion A is a slow reaction in which hydrogen peroxide reacts with
iodine that produces a chemical that looks like this: I3. This is
called triiodide. As soon as each triiodide chemical is produced,
it immediately gets consumed by Reaction B.
Reaction A: Hydrogen Peroxide + Iodine → Triiodide + Water
Reaction B is a fast reaction that uses vitamin C to change the
triiodide back to iodine, which keeps the solution clear.
Reaction B: Triiodide + Vitamin C → Iodine + Sulfur Derivative
Eventually, the vitamin C that is keeping the solution from turn-
ing blue runs out, and the triiodide chemicals are not being con-
sumed by Reaction B anymore. Now triiodide reacts with the
starch, and this results in the solution turning a dark blue.
Triiodide + Starch Starch → Complex (blue)
The competing reactions (Reactions A vs. B) explain the delayed
colour change in the experiment.
INTRODUCTION
A chemical reaction is a process in which one or more mol-
ecules react with each other and are changed into other mol-
ecules. These are a part of many of the things we use or benefit
from every day. For example, batteries, car engines, and plas-
tics all require chemical reactions. Since chemical reactions
are so significant in our lives, understanding how we can con-
trol them is very important. For example, this would help with
product safety and for getting the most out of the products that
use chemistry. The iodine clock reaction is a chemical reac-
tion that can teach the basic principles of controlling chem-
istry. The iodine clock reaction is when two clear liquids are
mixed, resulting in another clear liquid. After a few moments,
the liquid instantaneously turns dark blue. The reason that the
solution remains clear momentarily is because there are two
competing reactions: Reaction A and Reaction B (Figure 1).
Iodine Clock Reaction
Ava Suuronen1
1Westboro Academy, 200 Brewer Way, Ottawa, ON K1S 5R2
PURPOSE
The purpose of this experiment is to determine how changing different
variables can affect the rate of the iodine clock reaction. The variables
to be tested are:
1) Temperature
2) Concentration of vitamin C
3) Stirring
Figure 1.
