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Georgia Journal of Science

Article Title

EFFECT OF ACID STRENGTH AND TEMPERATURE ON ACTIVATION ENERGY FOR MUTAROTATION OF SUCROSE USING POLARIMETRY

Abstract

The mutarotation of sucrose in acid was studied using polarimetry. Optical rotation data was collected using hydrochloric, nitric, and acetic acid solutions using a Perkin-Elmer Polarimeter. Sucrose solutions were prepared in each acid immediately prior to use and the change in observed rotation was recorded using acid concentrations of 0.125 M, 0.25 M and 0.50 M. Several hours of data was collected for each run. Temperature effects were examined and each acid was tested at 12°, 20°, and 37°C. Observed rotation was expressed as specific rotation and plotted graphically to determine the rate constants for mutarotation. R2 values for the plots were typically 0.97 or higher indicating linearity. For each acid, the rate constants at 12°C, 20°C, and 37°C were also obtained to determine the activation energy. Rates of hydrolysis were consistent with acid strength with hydrochloric having a rate constant values of 1.4 x 10-3 , 2.5 x 10-3, and 4.4 x10-3 M-1 s-1 in in 0.125 M, 0.25 M , and 0.50 M HCl respectively. A similar trend was observed for nitric acid with rate constants of 1.8 x10-3, 3.5 x 10-3 and 6.2 x 10-3 in 0.125 M, 0.25 M , and 0.50 M HNO3. While minimal change in optical rotation was observed in water alone, a correlation between the rate of hydrolysis and acid strength was noted with nitric and hydrochloric acids significantly higher rate constants than acetic acid. For temperature effects, the rate constants in 0.50 M nitric acid were 9.3 x 10-4 and 6.2 x 10-3 at 12 °C and 20 °C respectively. An Arrhenius plot was prepared for nitric acid yielding an activation energy of 165 kJ mol-1. Additional data has been collected for both concentration and temperature and is being analyzed including the rate constants in acetic acid and data at 37 °C

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