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Color Changes in Indicator Solutions. An Intriguing and Elucidative General Chemistry Experiment

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César R. Silva , Renato B. Pereira and Edvaldo Sabadini

Instituto de Química, UNICAMP, Caixa Postal 6154, 13083-970 Campinas, São Paulo, Brazil

J. Chem. Educ., 2001, 78 (7), p 939

DOI: 10.1021/ed078p939

Publication Date (Web): July 1, 2001

Section:

History, Education, and Documentation

Abstract

The simple dilution of an aqueous solution of the indicator (In) bromocresol green is proposed as an intriguing experiment for students of chemistry. As the solution is diluted with water, its color changes strikingly from reddish to pale blue. These changes are related to changes in the absorption bands in the visible electronic spectra. The pK_In can be determined through the Henderson-Hasselbalch equation by plotting the pH values as a function of log([In^-]/[HIn]). The concentration, in mol L^-1, of the HIn species can be determined by measuring the absorbance at 440 nm and using the ε value determined from the Beer's law plot. [In^-] is calculated from the difference between the initial HIn concentration and the observed [HIn]. Students will be able to conclude that the dissociated fraction of a weak acid increases with dilution.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Laboratory Instruction

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Acids / Bases

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This article has been cited by 4 ACS Journal articles (4 most recent appear below).

Using Visible Spectrophotometers and pH Measurements To Study Speciation in a Guided-Inquiry Laboratory
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- Using Visible Spectrophotometers and pH Measurements To Study Speciation in a Guided-Inquiry Laboratory
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  A collective-effort, guided-inquiry laboratory investigation was developed for the second-semester general chemistry laboratory for the purpose of increasing student conceptual understanding of equilibrium and speciation phenomena. This investigation ...
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Color Changes in Indicator Solutions
E. Sabadini
Journal of Chemical Education2002 79 (9), 1071
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  Response to the question "Can an indicator solution change color upon dilution?"
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Another Hazard
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Color Changes in Indicator Solutions
Addison Ault
Journal of Chemical Education2002 79 (9), 1070
- Color Changes in Indicator Solutions
  Addison Ault
  Journal of Chemical Education2002 79 (9), 1070
  Addresses the question "Can an indicator solution change color upon dilution?"
  Abstract | Hi-Res PDF | PDF w/ Links