Please see the below information I pulled from a website on a chemical
experiment called the Iodine Clock Reaction. I saw this performed in
a freshman chemistry class I was in years ago and had a fun idea for a
practical joke. What I want to know is ?Can I take a solution of
this, enclose it in a sealed glass jar (like a fishbowl) with only two
electrical connections dipping into the solution, and then with the
use of a small battery force electrical current to flow into this
solution thus making this turn from clear to blue at will.? Ideally I
want a little sealed glass fish bowl that I can keep on my desk, then
attach a battery and a remote hand operated device, that way I can
click on the remote and make the glass bowl turn from clear to blue.
I thought it would be a neat trick to mess with people. I can work
out the remote and the electrical portion of what I want to do here,
but I do not have the chemistry knowledge to know if just by running a
electrical current through this solution if it will produce the effect
that I want. Also this needs to be long lasting. I do not want to
have to mix up a new batch of the solution every few days, weeks or
months. I would like it to sit on my desk for years, then at the
click of my remote be able to change from clear to blue. Thanks.
Iodine clock reaction
Materials to be used:
100 mL of Solution A (0.20 M H2SO4, 0.088 M H2O2)
100 mL of Solution B (0.0016 M Na2S2O3, 0.052 M KI,
starch)
H2SO4- sulfuric acid. It burns if touch the skin
The vapor burns also if inhalated
H2O2 - oxygen water
Na2S2O3 - sodium thiosulfate
KI potassium iodate
500 mL flask or beaker
The reaction itself is simple:
1) stir very well the 2 solutions
2) wait to see what is going to happen
3) all of a sudden the color changes to bluish back and forth.
4) Do not forget to observe the timing it happens.
You can change the conditions, as temperature and solutions concentrations.
Explanation
In the iodine clock reaction,as it is called usually, there 2 processes happening
at the same time.
The first is a slow reaction producing iodine:
H2O2(aq) + 2 I-(aq) I2(s) + 2 OH-(aq)
However, the iodine is never seen because of the second very fast process in which
it is immediately reduced back to colorless iodide ion:
I2(s) + 2 S2O32-(aq) 2 I-(aq) + S4O62-(aq)
Thus, iodine is slowly formed and then instantly converted back to
iodide ion until
all the thiosulfate ion (S2O32-) is used up. At that point the iodine
concentration
shoots up and the intense blue color of the starch-iodine complex
appears. The time required to reach this point depends on the rates of
the two reactions, and consequently on the concentrations of all the
reactants. Anything that accelerates the first
reaction will shorten the time. This increasing the concentration of iodide,
hydrogen peroxide, or acid (it neutralizes the hydroxide ion) will make time
shorter. On the other hand, increasing the thiosulfate concentration will have
the opposite effect; it will take longer for the iodine color to appear. |
