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2003
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December
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In the Laboratory
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Acid–Base Equilibrium in a Lipid/Water Gel
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Kristina K. Streb
Department of Chemistry, Ohio Northern University, Ada, OH 45810
Predrag-Peter Ilich
Department of Chemistry and Biochemistry, Loras College, Dubuque, IA 52004
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December 2003
Vol. 80 No. 12
p. 1464
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| Abstract |
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A new and original experiment in which partition of bromophenol blue dye between water and lipid/water gel causes a shift in the acid–base equilibrium of the dye is described. The dye-absorbing material is a monoglyceride food additive of plant origin that mixes freely with water to form a stable cubic phase gel; the nascent gel absorbs the dye from aqueous solution and converts it to the acidic form. There are three concurrent processes taking place in the experiment: (a) formation of the lipid/water gel, (b) absorption of the dye by the gel, and (c) protonation of the dye in the lipid/water gel environment. As the aqueous solution of the dye is a deep purple-blue color at neutral pH and yellow at acidic pH the result of these processes is visually striking: the strongly green-yellow particles of lipid/water gel are suspended in purple-blue aqueous solution. The local acidity of the lipid/water gel is estimated by UV–vis spectrophotometry. This experiment is an example of host-guest (lipid/water gel–dye) interaction and is suitable for project-type biophysics, physical chemistry, or biochemistry labs. The experiment requires three, 3-hour lab sessions, two of which must not be separated by more than two days.
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| Supplement |
Additional background information and additional bibliography, notes for the instructor, experimental details, problems and solutions, notes for the student, and a list of chemicals are available.
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 Contents |
Folder JCE2003p1464W containing JCE2003p1464W.doc (Microsoft Word), Fig1.cdx,
fig2.cdx, and fig3.cdx (ChemDraw)
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| Download |
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| More Information |
Citation |
Streb, Kristina K.; Ilich, Predrag-Peter. J. Chem. Educ. 2003 80 1464.
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Keywords |
Acid–Base Chemistry; Dyes / Pigments; Laboratory Instruction; Physical Chemistry; Polymer Chemistry
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History |
Created:
Last Updated: |
October 31, 2003
February 28, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
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December
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1464
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