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

Química Nova

Cortes, Mônica Souza¹  Universidade de São Paulo, São Carlos, Brasil¹  Ramos, Luiz Antônio¹  Cavalheiro, Éder Tadeu Gomes¹ 

关键词: acid-base chemistry;    instrumental methods;    spectrophotometric titrations.;   

DOI  :  10.1590/S0100-40422007000400045

学科分类：化学（综合）

来源: Sociedade Brasileira de Quimica

【 摘 要 】

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.

【 授权许可】

Unknown