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Complexometric Titrations: Competition of Complexing Agents in the Determination of Water Hardness with EDTA
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Abstract
The competition of complexing agents for the same metal ion and the formation of colored metal-ion complexes is demonstrated with the use of an overhead projector. This demonstration can be used to emphasize both the relevance of the relative values of formation constants in the complexation of metal cations and the applicability of complexometric titrations in quantitative chemical analysis.
The demonstration is based on the traditional determination of water hardness in which EDTA is used as the titrant that complexes Mg2+ and Ca2+ ions. The color change that signals the end of the titration represents the successful removal of the Mg2+ ions from the metallochromic indicator Calmagite. This removal is possible because the value of the formation constant of the [Mg(EDTA)]2- complex is about 3 orders of magnitude greater than that corresponding to the [Mg(Calmagite)]- complex. The color change from wine-red (metal-bound indicator) to blue (unbound indicator) can be seen clearly in a large classroom with the use of overhead projection.
Keywords (Audience):
First-Year Undergraduate / GeneralKeywords (Domain):
DemonstrationsKeywords (Feature):
Overhead Projector DemonstrationsKeywords (Subject):
EquilibriumCiting Articles
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This article has been cited by 7 ACS Journal articles (5 most recent appear below).
Complexometric Titration of Aluminum and Magnesium Ions in Commercial Antacids. An Experiment for General and Analytical Chemistry Laboratories
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Shui-Ping Yang and Ruei-Ying TsaiJournal of Chemical Education2006 83 (6), 906Few chemical experiments use the reagents from consumer products. Student interest in chemistry usually suffers from the lack of relevance to their daily lives. Ultimately this leads to insufficient student chemical problem-solving ability. A novel ...
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A Microscale Spectrophotometric Determination of Water Hardness
James S. Gordon , Stephanie Harman , Kristen Weiss and Brian PettegrewJournal of Chemical Education2001 78 (8), 1089A Microscale Spectrophotometric Determination of Water Hardness
James S. Gordon , Stephanie Harman , Kristen Weiss and Brian PettegrewJournal of Chemical Education2001 78 (8), 1089A spectrophotometric titration was performed to determine water hardness. The titration incorporated the traditional titration method employing EDTA as the titrant and calmagite as the indicator. The microscale experiment was carried out in a spectrometer ...
Reduction of Calcium Concentrations by the Brita® Water Filtration System: A Practical Experiment in Titrimetry and Atomic Absorption Spectroscopy
Kimberly G. Olsen and Lisa J. UlicnyJournal of Chemical Education2001 78 (7), 941Reduction of Calcium Concentrations by the Brita® Water Filtration System: A Practical Experiment in Titrimetry and Atomic Absorption Spectroscopy
Kimberly G. Olsen and Lisa J. UlicnyJournal of Chemical Education2001 78 (7), 941We have examined the ability of a popular water filtration system to decrease the calcium concentration of solutions passed through the filter. The students' current interest in environmental and medical issues, combined with the scientific examination of ...
Development of Multianalyte Sensor Arrays Composed of Chemically Derivatized Polymeric Microspheres Localized in Micromachined Cavities
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Adrian Goodey, John J. Lavigne, Steve M. Savoy, Marc D. Rodriguez, Theodore Curey, Andrew Tsao, Glen Simmons, John Wright, Seung-Jin Yoo, Youngsoo Sohn, Eric V. Anslyn, Jason B. Shear, Dean P. Neikirk, and John T. McDevittJournal of the American Chemical Society2001 123 (11), 2559-2570The development of a chip-based sensor array composed of individually addressable polystyrenepoly(ethylene glycol) and agarose microspheres has been demonstrated. The microspheres are selectively arranged in micromachined cavities localized on silicon ...
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- Received: August 03, 2009
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