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Eclética Química

Print version ISSN 0100-4670

Abstract

CUCHINSKI, Ariela Suzan; CAETANO, Josiane  and  DRAGUNSKI, Douglas C.. Extraction of the dye of beet (Beta vulgaris) for use as indicated in acid-base. Eclet. Quím. [online]. 2010, vol.35, n.4, pp.17-23. ISSN 0100-4670.  http://dx.doi.org/10.1590/S0100-46702010000400002.

In this study, we investigated the behavior of aqueous and alcoholic extract of sugar beet (Beta vulgaris) as an acid-base indicator, having as main objective the awakening interest in the use of natural indicators as an alternative to teaching of concepts of titration, equilibrium chemical and the law of Lambert-Beer. For the experiments we used standard solutions of hydrochloric acid (HCl), acetic acid and sodium hydroxide (NaOH). Initially tests were performed to evaluate and reversibility of the system, and it was observed that the color changes from red to yellow with the addition of base and returns to red with acid addition, so can be used to explain the chemical equilibrium. The analysis of UV-vis spectra showed that the molecular absorption in the visible region, have different characteristics, giving evidence that was altered structure of the indicator in acidic and basic medium. After the titration was found that the points of equivalence with the natural indicator showed concordance with those obtained by potentiometric method. Furthermore, the aqueous and alcoholic extract of beet has a good correlation for Beer-Lambert law, being that the acidic medium presented a better correlation compared with basic.

Keywords : beet; titration; natural indicator.

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