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Tammy Rodriguez Lab ID: 92216 38565834 The Kinetics of Bleaching Blue #1 Dye Abstract 2.5mL of both 0.37M bleach and 0.74M bleach were reacted with 7.5mL 8.0x10 -7 M Blue #1 dye to spectrophotometrically determine reaction order of both reactants and reaction rates. Both reactants had a reaction order of 1. The rate for the 0.37M bleach was 1.87x10 -7 M/s , and 3.73x10 -7 M/s for the 0.74M bleach. Introduction Like previous experimentation on dye and bleach reaction kinetics, this experiment used a spectrophotometer to measure reaction rate through the decreasing absorbance value of blue dye throughout the reaction (Ganley, 2015). Kinetic traces of the reactions were obtained to determine reaction order. First order reactions are identifiable by straight lines of best fit in the ln(absorbance) vs time graphs. To determine the reaction order with respect to bleach as well as the relationship between increasing reactant concentration and reaction rate, two different bleach concentrations were used, 0.37M and 0.74M. Both bleach concentrations were in excess, allowing the reaction order with respect to dye to be determined from kinetic traces. Reaction rate was predicted to increase as reactant concentration increased, per the hypothesis. The slope of a Beer’s Law graph, where absorbance is equal to (molar absorptivity constant)(path length)(concentration), was used to determine instantaneous concentration of dye at any absorbance value. Instantaneous dye values were then used to determine any instantaneous rate, as the reaction constant and concentration of bleach were constant. Procedure 7.5mL of 8.0x10 -6 M Blue #1 dye and 2.5mL of 0.37M bleach were found to have the required reaction time of around 2 minutes. First calibrated with a blank, a spectrophotometer found the analytical wavelength of the dye to be 0.615nm. Part 1:Using a serological pipet, 7.5mL 8.0x10 -6 M Blue #1 dye was added to five glass vials. The spectrometer was set up with the appropriate wavelengths, and a blank was run. One at a time, vials were wiped of any fingerprints using kimwipes, and placed into the spectrophotometer. A metallic stir bar was added. 2.5mL of 0.37M bleach, obtained with a syringe, was added to the vial. The vial was capped, and the program was run and stopped when the absorbance reading was at around 0.2. The k’ value was recorded. An average k’ value was determined. This was repeated a total of five times. Part 2: The process from the above paragraph was repeated using 0.74M bleach. Solutions of 100%, 80%, 60%, 40% and 20% dye were made. The spectrophotometer was calibrated with a blank, all vials were carefully wiped, and a calibration plot was obtained. Results Table #1: k Values Table #2: Reaction Rate Table 4: Reaction Rate at Two Points K Value Rate Abs Inst [dye] Inst Rate Individual Part 1 Part 2 Part 1 1.87x10 -7 M/s Part 1 0.6 2.19x10 -6 M 6.83x10 -8 M/s 0.3360M -1 s -1 0.3268M -1 s -1 0.3 1.09x10 -6 M 3.42x10 -8 M/s Class Avg 0.3294M -1 s -1 Part 2 3.73x10 -7 M/s Note: Part 1 indicates the reaction which used 0.37M bleach, Part 2 indicates 0.74M bleach.

Tammy Rodriguez Lab ID: 92216 38565834 Discussion Rate approximately doubled when the concentration of bleach was doubled, supporting the hypothesis that there is a positive relationship between reactant concentration and reaction rate. The rate constant for the reaction with 0.37M bleach was 0.3360M -1 s -1 , and 0.3268M -1 s -1 for the reaction with 0.74M, while the class average was 0.3294M -1 s -1 . The first k value had a difference of 0.0066M from the class average, while the 0.74M bleach reaction had a difference of 0.0026M. Inconsistencies may have been due to inexact/imprecise amounts of dye and bleach used, as a serological pipet rather than a volumetric pipet was used to measure the dye, and a simple syringe was used to measure the bleach. More precise glassware might reduce the range of these inconsistencies, as it could make the measured reactant amounts more accurate to the desired 7.5mL of dye and 2.5mL of bleach.However, overall the deviation between the class average and experimental k values was minimal, and the actual k value is likely to be somewhere around 0.3300M -1 s -1 . Both dye and bleach were found to have a reaction order of 1, as their kinetic traces had straight lines of best fit only for the graphs with ln(absorbance) on the y axis. The reaction rate increased by around two in the 0.74M bleach reaction because the concentration was doubled from 0.34M, and the reaction is first order with respect to bleach. Calculated instantaneous reaction rates also followed this trend, with the greater absorbance value, and thus greater concentration of dye having a larger reaction rate than the smaller absorbance value. Reaction rate approximately halved when absorbance rate and dye concentration halved, supporting the conclusion that the reaction is first order with respect to dye as well. Lastly, to eliminate sources of error, gloves should be worn to avoid leaving fingerprints on the vials that could interfere with the spectrophotometer. Conclusion The objective of this study was met as reaction orders and the rates were determined. Reaction rate increased when the concentration of bleach, a reactant, increased. Both reactants had reaction orders of 1. The rate for the reaction with 0.37M bleach was 1.87x10 -7 M/s, and 3.73x10 -7 M/s for the reaction with 0.74M bleach. Bibliography Ganley, J. C. A homogeneous Chemical Reactor Analysis and Design Laboratory: The reaction kinetics of Dye and Bleach. Education for Chemical Engineers 2015 , 12 , 20–26.