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

Quimica nova

Cortes, Mônica Souza¹  Ramos, Luiz Antônio¹  Cavalheiro, Éder Tadeu Gomes¹ 

[1] Universidade de São Paulo, São Carlos, Brasil

关键词: acid-base chemistry;    instrumentalmethods;    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 bythe variation of the pH of the medium, the use of these different colors inorder to demonstrate principles of spectrophotometric acid-base titrations usingthe crude extracts as indicators is proposed. The experimental setup consistedof a simple spectrophotometer, a homemade flow cell and a pump to propel thefluids along the system. Students should be stimulated to choose the best wavelengthto monitor the changes in color during the titration. Since the pH of the equivalencepoint depends on the system titrated, the wavelength must be properly chosento follow these changes, demonstrating the importance of the correct choiceof the indicator. When compared with the potentiometric results, errors as lowas 2% could be found using Rhododendron simsii (azalea) or Tibouchinagranulosa (Glory tree, quaresmeira) as sources of the crude extracts.

【 授权许可】

CC BY