| My partner and I must do a demonstration for our
AP chemistry class on 3/19. We have chosen to do
a breathalyzer reaction. We are going to compare
how the indicator reacts with vodka to its
reaction with beer. We have all the materials,
and we have followed the directions carefully.
However, we have had major problems getting the
reaction to occur quickly and noticeably enough.
We have had problems with step 3 (getting the
gel) and 16 (making the reaction happen).
Initially, the reaction was slow. The mixture we
used was supposed to turn from orange to green.
Instead, it turned from yellow to clear with some
blue tints, taking over ten minutes to complete.
After experiencing this twice, I added a few
more drops of potassium dichromate and was able
to make the gel orange. When I added ethanol
(about five drops of vodka), the reaction was
slightly more noticeable. Putting several drops
of the ethanol directly onto the gel changed it
to green/blue in a minute or two. This was
better, although still not fast enough. My
partner and I tried again to see if we could make
the reaction faster by adding even more potassium
dichromate solution. Instead of obtaining the
desired orange gel as I had done before, the
mixture was mostly a yellow liquid with only
slight gelling. Adding more sulfuric acid and
sodium silicate did not seem to help. My
partner and I need to get the reaction working
well very soon so that we can have an interesting
demonstration for the class. We are looking for
a gel that will completely turn green in a pipet
in about a minute when ethanol from a balloon is
blown into it. We would like to compare this
with adding beer through the balloon. Why did
the mixture stop gelling and turning orange
despite all the trials and adjustments? What can
we do to get an orange gel that will work well,
as I described?
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Answer 1:
Thank you for your careful description of your
problem. Often times being careful is the key to
scientific success.
Having said that, I'm
afraid that I do not have a clear answer to your
problem, but you may wish to consider the
following items. Your difficulties seem to be
largely in that the rates of certain chemical
reactions are not as high as you need them to be.
You might want to think about what makes
reactions go faster. Some things include:
increasing temperature, increasing concentration,
and changing pH. By varying these (and perhaps
other parameters) you may be able to get the
reaction to work.
Even if these things don't
work, you might want to keep them in mind for
future cases where you need to accelerate
reactions.
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