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Nearly every demonstration of "chemical magic"
involves the classic Blue Bottle. This demonstration has
been reported in numerous places including Alyea and Dulton
(1) and Summerlin and Ealy (2) and involves the alkaline
glucose reduction of methylene blue. Even though this is a
very simple demonstration it fascinates audiences,
especially those of middle-school age and younger.
We have found other indicators that may be added
to the classic Blue Bottle to produce a rainbow of colors.
Some of these indicators are listed in Table 1.1
Table 1. Combination of Indicators and Their Colors in the Oxidized and Reduced Forms
| Indicator(s) |
Oxidized |
Reduced |
| o-Cresolsulfonphthaleina/methylene blue |
purple |
violet |
| Phenolphthalein/methylene blue |
purple |
red to pinkb |
| Methyl red/methylene blue |
green |
yellow |
| Methlene blue |
blue |
colorless |
| Titan yellowc/methylene blue |
drab green |
green |
| Azo violet/methylene blue |
purple |
light violet |
| Phenol red/methylene blue |
purple |
red |
a Also known as o-cresolphthalein or cresol red.
b Pheonolthalein also undergoes a reduction under these conditions, but at a much slower rate. The phenolphthalein/methylene blue starts out intensely red; with each cycle it becomes lighter until it is pale pink in the reduced form.
c Also known as Clayton yellow.
Materials
- Seven 250-mL Florence (or Erlenmeyer) flasks with tight-fitting stoppers
- Indicators2
- 800 mL of 0.7 M potassium hydroxide solution
- 30 g of dextrose (glucose)
- 5% sodium hydroxide solution
Procedure
Prepare 800 mL of 0.7 M potassium hydroxide
solution. To this add one or more crystals of methylene blue to
just obtain a royal blue colored solution.3 Do not add too much!
Caution: Potassium hydroxide solutions are
very corrosive and can lead to severe burns if spilled
upon the skin.
To one flask add about 200 mL of the potassium
hydroxidemethylene blue solution. To each of the
remaining 6 flasks add about 100 mL of water and 35 drops of
5% sodium hydroxide solution. Then to each of the 6 flasks
add the chosen indicator until the solution is the color
desired for the reduced solution3 (again, do not add too much).
Add 5 g of glucose to each of the 7 flasks, and 120
mL of the methylene blue/potassium hydroxide solution to
the 6 flasks with the additional indicator. Stopper the
flasks and allow to stand. The color of the oxidized solution
will slowly change to that of the reduced solution (the color
of the indicator in base).
The color of the oxidized solution can be
regenerated by giving the flask a few vigorous shakes. (The stopper
will need to removed periodically to allow a fresh supply of
oxygen into the flask.)
We have found this to be an effective addition to
our presentations of "chemical magic" that the department
gives annually to 5th and 6th grade students in the area.
Notes
1. See page 361 for color pictures of the oxidized and
reduced forms of the first six methylene blue-indicators listed in Table 1.
2. All of the indicators used here can be obtained from
Aldrich Chemical Company, Inc.
3. For the methylene blue solution, the intense royal blue
color requires 10 mg of the indicator; for the other solutions about 1
mg is required. It is important that none of the solutions be so
intense as to mask the other.
Literature Cited
1. Tested Demonstrations in Chemistry, 6th ed. Alyea, H. H.;
Dutton, F., Eds.; Journal of Chemical Education; Easton, PA, 1965, pg 187.
2. Summerlin, L. R; Ealy, J. L., Jr. Chemical Demonstrations: A
Source Book for Teachers; American Chemical Society: Washington,
DC, 1985; p 93.
See Letter re: this article.
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Citation
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