Abstract
The study was carried out to describe the kinetics and thermodynamics of hydrogen peroxide oxidation of a typical food dye (Tartrazine). The effect of different operational factors were investigated spectrophotometricallyat wavelength460 nm under pseudo first order reaction.These included concentration of the oxidant and the dye, the pH, ionic strength and temperature of the reacting medium and the presence of transition metal ion as homogenous catalyst. A complete and smooth decolourisation was observed. The results showed that the rate of oxidation of dye increased with increasing in concentration of substrate and oxidant. Increasing in temperature, ionic strength and pH of the basic reaction medium also raised the reaction rate. The rate of oxidation also increased with increasing in the concentration of Fe (III) ion. Pseudo second order rate constant (k2) obtained was 1.95 x 10-3 M-1s-1 and 3.8 x10-3M-1s-1 in the absence and presence of Fe (III) ion respectively. The Arrhenius activation energy for the oxidation in the absence and presence of Fe (III) ion were 47.23 kJmol-1 and 42kJmol-1 respectively. Other thermodynamic parameters showed entropy of activation (ΔS#), free energy of activation (ΔG#) and Enthalpy of activation of the reaction (ΔH#) in the presence of Fe (III) as -34.7 JK-1mol-1, 48.4 kJmol-1 and 40.30 kJmol-1 respectively. The results in the absence of Fe (III) ion were -24.6 JK-1mol-1, 51.2 kJmol-1 and 44.0 kJmol-1respectively. The relative lower activation energy (Ea),fairly higher negative value of (ΔS#) and higher (ΔG#) , with higher rate constant in the presence of Fe(III) ion showed Fe(III) ion enhancement of rate of decolourisation.
 Keywords: Tartrazine Food dye, Kinetics, Thermodynamics, Hydrogen Peroxidede colourisation,
Highlights
Research work describes the potential of Hydrogen peroxide in the oxidative decolourisation of tartrazine - a typical food additive
Kinetic Measurement: Since change in concentration was monitored with spectrophotometer, the wavelength corresponding to the maximum absorbance (λ max) need to be ascertained from the absorption spectrum
Effect of varying Substrate (Dye) Concentration: The dependence of the reaction rate on Tartrazine concentration was measured by maintaining constant the other variables such as the concentration of oxidant solution and the medium ionic strength, temperature, pH
Summary
Chemical reagents used in this study were hydrogen peroxide, Iron (III) chloride, tartrazine dye, sodium hydroxide, bicarbonate and sodium chloride salt, hydrochloric acid. Kinetic Measurement: Since change in concentration was monitored with spectrophotometer, the wavelength corresponding to the maximum absorbance (λ max) need to be ascertained from the absorption spectrum. The specific rates were evaluated for the reaction were obtained from plots of logarithm of absorbance (A) against time (t).The average initial rates kobs over three independent measurements were determined by linear regression from the slope of the concentration versus time plots. Wherek was the rate constant for the bimolecular reaction of Tz and H2O2, a and b were pseudo-order of the reaction with respect Tz andH2O2, the absorbance A at 640nm was proportional to the concentration of Tz. The slope of the ln A vs time defined the pseudofirst order rate constant kobs was determined. The quantities of testing parameter were varied while maintaining constant the amount of each of all other components in the system
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