In the Classroom edited by
Overhead Projector Demonstrations
Doris K. Kolb
The Blue Bottle Experiment—Simple Demonstration of Self-Organization
Bradley University Peoria, IL 61625
ˇ cík L’ubica Adamˇ cíková and Peter Sevˇ Department of Physical Chemistry, Comenius University, 842 15 Bratislava, Slovak Republic
The “blue bottle” experiment involves the alkaline glucose reduction of methylene blue (1–3). Upon standing, the solution turns colorless indicating that the dye has been reduced by the glucose. Shaking the flask will cause the blue color to return as the methylene blue is oxidized by atmospheric oxygen to its blue form. The experiment is very entertaining and has been presented in the scientific education literature as an introductory demonstration in the discussion of chemical kinetics. We have found that pattern formation can be seen when a solution containing NaOH, glucose, and dye is poured into an open Petri dish. For classroom demonstrations, the Petri dish can be placed on an overhead projector. Materials Petri dish The following solutions: 1 M NaOH 0.5 M glucose (or galactose, xylose, arabinose or mannose) 10᎑3 M dye (methylene blue or toluidine blue)
Procedure Mix 5 mL of 1 M NaOH, 1.6 mL of 0.5 M glucose, 0.5 mL of 10᎑3 M dye, and 2.9 mL of water and pour the mixture into a Petri dish to a depth of 2 mm or more. It remains blue for ~2–4 min; then small colorless regions appear and subsequently grow, forming mosaic structures. If the Petri dish is protected from air with a glass cover, no pattern formation is seen in the reaction mixture. Stirring the liquid in the Petri dish produces a homogeneous blue coloration. Upon standing, within a few minutes, the blue liquid reverts to its original pattern. This process can be repeated many times. The patterns are transient because the system evolves towards thermodynamic equilibrium. The
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Figure 1. Pattern in a Petri dish filled to a height of 2 mm with a solution containing NaOH, glucose, methylene blue, and some drops of indicator (phenolphthalein), 4 min after the start of the experiment.
patterns disappear after about 2–3 hours, when a homogeneous pale violet state is reached. A more interesting color change is observed when an indicator such as phenolphthalein is added (Fig. 1).1 Note 1. Figure 1 is printed in color on page 1509 of this issue.
Acknowledgment This work was supported by Grant No. 1/4009/97 from the Scientific Grant Agency of MESR. Literature Cited 1. Campbell, J. A. J. Chem. Educ. 1963, 40, 578. 2. Cook, A. G.; Tolliver, R. M.; Williams, J. E. J. Chem. Educ. 1994, 71, 160. 3. Vandaveer, W. R., IV; Mosher, M. J. Chem. Educ. 1997, 74, 402.
Journal of Chemical Education • Vol. 75 No. 12 December 1998 • JChemEd.chem.wisc.edu
