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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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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,
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

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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/ s00897020619b

Issue date: December 1, 2002

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