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A Colorful Ion Exchange Experiment
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Abstract
A colorful ion-exchange experiment is described. The use of a resin with an adsorbed acid-base indicator allows students to follow the progress of the ion-exchange front along the column. In parallel, students can follow the ion-exchange breakthrough curve using a continuous conductometric cell at the column outlet. In the present example, K+ (KCl) exchanges with H+ (HCl) in a strong cationic resin (Amberlite IR 120). The adsorbed indicator is methyl violet. Sorption equilibrium is favorable to the K+ ions.
Monovalent ions, used in this experiment, have the disadvantage of usually being colorless (except perhaps permanganate, but this is an extremely strong oxidant which attacks the resin). On the other hand, many divalent ions are colorful but the shape of the concentration front is hard to explain qualitatively as well as quantitatively. That is because the shape of the front depends on the total ionic concentration. However, color can be introduced in a monovalent ion-exchange system by adding an appropriate acid-base indicator to the resin.
The text describes this experiment qualitatively. A simplified quantitative description, using the solute movement theory, can be found online.
Keywords (Audience):
Second-Year UndergraduateKeywords (Domain):
Laboratory InstructionKeywords (Pedagogy):
Hands-On Learning / ManipulativesKeywords (Subject):
Ion ExchangeCiting Articles
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This article has been cited by 1 ACS Journal articles (1 most recent appear below).
Carbon Dioxide Absorption in a Membrane Contactor with Color Change
Inês Pantaleão, Ana F. Portugal, and Adélio Mendes, Joaquim GabrielJournal of Chemical Education2010 87 (12), 1377-1379Carbon Dioxide Absorption in a Membrane Contactor with Color Change
Inês Pantaleão, Ana F. Portugal, and Adélio Mendes, Joaquim GabrielJournal of Chemical Education2010 87 (12), 1377-1379A pedagogical experiment is described to examine the physical absorption of gases, in this case carbon dioxide, in a hollow fiber membrane contactor (HFMC) where the absorption concentration profile can be followed by a color change. The HFMC is used to ...
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- Received: August 03, 2009
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