TCE     
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The Chemical Educator
ISSN: 1430-4171 (electronic version)
Abstract Volume 7
Issue 6 (2002) pp 359-363
A Colorful Investigation of a Diprotic Acid: A General Chemistry Laboratory Exercise
Eugene T. Smith and John R. Matachek
Department of Chemistry, Hamline University, St. Paul, MN 55104, gsmith@gw.hamline.edu
Received April 26, 2002. Accepted August 5, 2002
Published online: 1 November 2002
Abstract. A general chemistry
laboratory experiment that can be completed in a single laboratory period
is described that familiarizes students with the acid–base chemistry
of a diprotic acid and with the use of visible spectroscopy to determine
species concentrations. This experiment is a modified version of a previously
described laboratory exercise developed for an upper-division quantitative
analysis course. Students work in teams and as a class to generate different
ionization states of various highly absorbing dyes. Both spectroscopic
and potentiometric (pH) data is collected using LabWorks II stations,
but other inexpensive pH meters and visible spectrometers (e.g., Spec
20s) are suitable. A spreadsheet template is used to determine the percent
composition of various ionization states of a diprotic acid and to determine
the pKa values. Besides introducing students to
fundamental tools and key chemical concepts, this laboratory is also
inexpensive to operate and utilizes nontoxic, colorful solutions.
Key Words: Laboratories and Demonstrations; general chemistry; acid–base chemistry; pKa determination; Beer's law for mixtures
(*) Corresponding author. (E-mail: gsmith@gw.hamline.edu)
Article in PDF format (332 KB) HTML format
Supporting Materials:
A laboratory handout for students and the Excel worksheets that produced Figures 5–8 are available in a Zip file (116 KB) 10.1007/ s00897020619bIssue date: December
1, 2002
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