Prosiding Seminar Kimia Bersama UKM-ITB VIII 9-11 Jun 2009 535 KINETICS OF THE OXIDATION OF VITAMIN C SITTI RAHMAWATI, * BUNBUN BUNDJALI ** * sittirahmawati@yahoo.com , bunbun@chem.itb.ac.id ** Inorganic and Physical Chemistry Division FMIPA, Institut Teknologi Bandung, Indonesia ABSTRACT Vitamin C or ascorbic acid is necessary for the human body, although only in small quantities. Ascorbic acid is acquired through food, as the human body cannot synthesize ascorbic acid. Vitamin C is a kind of vitamin that can be found in fruit and vegetables. There are many advantages we can find in vitamin C. First, vitamin C helps and preserves colagen structure. Second, vitamin C has a role as antioxidant. Third, vitamin C is needed for activation of various enzym. Fourth, vitamin C can increase the absorption of ferum, calcium, and folat acid. Vitamin C is very easily decomposed by increases in temperature, ascorbic acid will be oxidized to become L-dehydroaskorbat acid. This is hard to prevent in foodstuff processing of which contains vitamin C, such as vegetables and fruits. This research aims to determine the kinetics of oxidation of ascorbic acid due to an increase in temperature (40 0 C – 80 0 C) and to create an ascorbic acid oxidation reaction laboratory module to be applied in the senior high school reaction kinetics curriculum. The determination of the kinetics of the oxidation of ascorbic acid applies the integral and half-change time methods, while the concentration of the remaining ascorbic acid in sixty minute intervals is determined by iodimetric titration method. Decomposition of ascorbic acid is measured at 40 0 C, 50 0 C, 60 0 C, 70 0 C and 80 0 C. The results of this research indicate that at 40 0 C, 50 0 C, 60 0 C, 70 0 C and 80 0 C the kinetics of the oxidation of ascorbic acid is a first-order reaction with a rate constants of 4.55 x 10 -4 minute -1 , 5.85 x 10 -4 minute -1 , 8.4 x 10 -4 minute -1 , 1.1 x 10 -3 minute -1 and 1.015 x 10 -3 minute -1 , respectively. The activation energy and the pre-exponential factor for the oxidation of ascorbic acid were found to be 20.73 kJ. mol -1 and 1.372 minute -1 . The procedure used in this study was modified into a laboratory module to be applied in the teaching of reaction kinetics at the senior high school level.