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It
has been reported that, under special conditions, U.S. coins can interact to form
moneycules ,
clusters of coins held together by greed. |
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Methylene Blue
is a dye used in biological staining. Its formula is on the left.
Note the extended double bond structure which allows electronic
absorption in the visible region. What color light is absorbed? Note also the blue ionic structure is stabilized by allowing the + charge to be distributed on the two nitrogens attached to the ring system (to become partial "ammonium ions") as well as the ring sulfur. When reduced, it forms "leucomethylene blue which is colorless. The highest energy electrons are now more restricted in space. In this experiment, glucose will be the reducing agent. This reaction takes place at a measurable rate. |
Phenolphthalein
is a common indicator. It was also used as a laxative through
almost all of the twentieth century. Although it rapidly turns from colorless in acids to red in base, curiously it also slowly turns back to colorless at a measurable rate in very concentrated base. |
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Note from the above formulas,
the red color of phenolphthalein in weaker base which is caused by the
absorption of mainly green light is supported by the extended conjugated
double bond system. However the reaction of a hydroxide ion with
the phenolphthalein ion under very strongly basic conditions adds a HO
group to one of these double bonds and significantly reduces the degree
of "conjugation" (i.e. the highest energy electrons have
become restricted to a smaller volume) This means that the energy between the highest occupied orbital and the lowest vacant orbital increases and the molecule becomes colorless. It takes more energy than is in any quantum of visible light (even blue) to cause this electronic transition. |
© RW Kluiber 4/1/2004