Resumo

NAVAS, Petra Beatriz  e  CARRASQUERO-DURAN, Armando. Introduction to the chemicals kinetics: effect of a vegetabl extract on the oxidation mechanism of fe(ii). Paradìgma [online]. 2008, vol.29, n.2, pp.81-96. ISSN 1011-2251.

The kinetics study of iron(II)ophenantroline oxidation induced by HNO₃ is proposed as a didactic experience for the course of chemical kinetics. Three didactic moments are included: First, review of related chemical concepts and design of the concept maps and the experiments. Experimental results are obtained and used to prove validity of proposed reaction mechanisms. Transformation of ferrous ion to ferric ion was followed by changes in absorbance of red colored ophenantroline complex. It was observed a pseudo first order kinetics with a velocity constant of 0,050 ± 0,002s^-1. Oxidation rates were lower when an orange albedo extract was added to reaction mixture, which was associated with the presence of flavonoids in the natural extract. This inhibitory effect was associated with a reaction rate of -1 in natural extract concentration keeping the first order in the bivalent ion. Steady state method, integrated equations and Van´t Hoff method proven to be valuable for the kinetic study. The experience may be very useful to introduce the students in the most important concepts and models of the chemical kinetics at the university level.

Palavras-chave : Kinetics; mechanism; oxidation; inhibitor; albedo; ferrousion.