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(Reference retrieved automatically from SciELO through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Spectrophotometric titrations of acid-base systems using flower extracts containig anthocyanins

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Author(s):
Mônica Souza Cortes [1] ; Luiz Antônio Ramos [2] ; Éder Tadeu Gomes Cavalheiro [3]
Total Authors: 3
Affiliation:
[1] Universidade de São Paulo. Instituto de Química de São Carlos - Brasil
[2] Universidade de São Paulo. Instituto de Química de São Carlos - Brasil
[3] Universidade de São Paulo. Instituto de Química de São Carlos - Brasil
Total Affiliations: 3
Document type: Journal article
Source: Química Nova; v. 30, n. 4, p. 1014-1019, 2007-08-00.
Abstract

Considering the attraction of the students' attention by the changes in the colors of vegetable crude extracts caused by the variation of the pH of the medium, the use of these different colors in order to demonstrate principles of spectrophotometric acid-base titrations using the crude extracts as indicators is proposed. The experimental setup consisted of a simple spectrophotometer, a homemade flow cell and a pump to propel the fluids along the system. Students should be stimulated to choose the best wavelength to monitor the changes in color during the titration. Since the pH of the equivalence point depends on the system titrated, the wavelength must be properly chosen to follow these changes, demonstrating the importance of the correct choice of the indicator. When compared with the potentiometric results, errors as low as 2% could be found using Rhododendron simsii (azalea) or Tibouchina granulosa (Glory tree, quaresmeira) as sources of the crude extracts. (AU)