Kinetics Lab

Introduction

        The kinetics lab was conducted in order to determine the rate law and activation energy for the bleaching of brilliant blue dye. In order to accomplish this, colorless solutions created as a product of the decomposition of the dye, a spectrometer and Beer’s Law were utilized. Additionally, two different temperatures and the two-point form of the Arrhenius equation were utilized to determine the reaction’s activation energy.

Results and Discussion

Two experiments, one using room temperature 294.9 K and the other using 318 K, were performed using the initial concentration of M brilliant blue dye and 0.0244 M sodium hypochlorite.                     [pic 2][pic 3][pic 1]

The spectrometer was set to a wavelength of 630 nm then was blanked with DI water.

        For the first experiment, in a small beaker 5.0 mL of brilliant blue solution with 5.0 mL of the sodium hypochlorite were mixed. This mixture was put into a cuvette and a timer was started. Intervals of two minutes were timed until ten data points were collected. At each two minute mark, the time and absorbance were recorded. The concentration for each absorbance was found using this form of Beer’s Law (A=ElC):    [pic 4]

 [pic 5]       [pic 6]       [pic 7][pic 8]

[pic 9][pic 10]

        For the second experiment, the same steps for the first experiment were followed, but once the mixture was inserted into the cuvette, it was put into a water bath. At measured intervals of two minutes, the cuvette was taken out, dried, measured and the absorbance and the time were recorded. Once this is done the cuvette was returned to the water bath.

                                                     [pic 11][pic 12]

Finally, the results from the two different temperatures and the two-point form of the Arrhenius equation: [pic 13], were used to determine the reaction’s activation energy which was determined to be . The rate law equation,[pic 15], and graphs were used to determine x and y in the rate law. The order of the reaction with respect to  was determined to be first order. The overall rate law at room temperature is , and the overall rate at 45˚C is .[pic 14][pic 16][pic 17][pic 18]