Exp8 Kinetics of SN1 Solvolysis with tert-Butyl Chloride 2123-18 AR

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Medical Academy for Science and Technology**We aren't endorsed by this school

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BIO 1025

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Chemistry

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Jan 28, 2024

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OCHEM 2123-18 Experiment 8: Kinetics of SN1 Solvolysis with tert-Butyl Chloride Introduction During this experiment, we studied the kinetics of SN1 solvolysis with tert-butyl chloride to learn the reaction mechanism and the factors that influence the rate of reaction. SN1 solvolysis is a type of unimolecular, nucleophilic substitution reaction that involves the cleavage of a carbon-halogen bond with the subsequent formation of a carbocation intermediate. The purpose of this lab was to investigate the kinetics of SN1 solvolysis with tert-butyl chloride while focusing on the rate-determining step and the factors that influence the rate. Our objective is to determine the order of the reaction with respect to tert-butyl chloride and measure the reaction rates to identify if they support or contradict the rate behavior predicted by the SN1 reaction model. For our prelab questions, the reaction with the nucleophile is the Sn1 reaction, while the one with the base is the Sn2 reaction. The t-butyl alcohol will react the fastest with HCl to form the corresponding alkyl chloride via an Sn1 pathway. It is true that the rate of a first order chemical reaction is proportional to the concentration of the electrophile. Observations and Experimental Throughout our lab, we were able to see the titration of NaOH into tert-butyl chloride. For this experiment we used a buret attached on a ring stand with a buret clamp with 0.1 M NaOH to the 0 mark, bromothymol blue indicator, a 250mL Erlenmeyer flask filed with 50 mL

of 43% EtOH/57% H2O, 10 mL of 0.2 M tert-butyl chloride/acetone, a hot plate, hot water bath, thermometer, stirrer, stir bar, ice bath and room temperature water bath. When beginning our experiment, the 50 mL of 43% EtOH/57% H2O were tested with 5 drops of bromothymol blue indicator to test its pH, once tested, it was found to be acidic due to its yellow color change rather than a blue basic reaction. As we placed the tert-butyl chloride/acetone into the flask, the solution turned yellow. We ensured to cover our flask with Parafilm to prevent any solution evaporation. We turned on the stirrer to about 100rpm to moderately stir the mixture without blending CO2 into the reactant mixture which could lower the pH. As we assed 0.5mL of NaOH to the mixture every time, we times how long it took for the clear NaOH to turn the solution from yellow to blue and then back to yellow again due to the neutralization. Once all 3.5 mL of NaOH were titrated into the solution it was still a yellow hued color and then placed into the hot water bath. Then we placed it into the cold water bath and proceeded to titrate the NaOH drop wide until the indicator turns a light blue. Results, Calculations, and Discussion The experiment aimed to investigate the kinetics of SN1 solvolysis with tert-butyl chloride (t-BuCl) by monitoring the reaction over different time intervals following the addition of sodium hydroxide (NaOH). The data table below summarizes the key results obtained during the experiment. Kinetic Data Time (s) Added base (mL) Added base NaOH (mol) Amount tBuCl reacted (mol) [tBu-C]t ln

(mL → L x 0.1M NaOH) 23 0.50mL 0.000005 mol 0.000005 mol 0.00000515 ln(0.00000515) = -12.17 36 1.0mL 0.00001 mol 0.00002 mol 0.000015 ln(0.000015) = -11.12 84 1.5mL 0.000015 mol 0.000010 mol 0.000020 ln(0.000020) = -10.81 101 2.0mL 0.00002 mol 0.00001 mol 0.00003 ln(0.00003) = -10.41 118 2.5mL 0.000025 mol 0.000035 mol 0.000050 ln(0.000050) = -9.90 130 3.0mL 0.00003 mol 0.00003 mol 0.000075 ln(0.000075) = -9.49 158 3.5mL 0.000035 mol 0.000025 mol 0.00015 ln(0.00015) = -8.80 Scatter Plot Graph The experiment involved additions of NaOH at specific time intervals, with measurement of the resulting volume and calculation of moles of added NaOH. The concentration of t-BuCl at each time point was determined by considering the moles of t-BuCl reacted and the total reaction volume. Natural logarithms of t-BuCl concentrations were also calculated for further analysis. The amount of t-BuCl reacted increased with time, indicating the progression of the SN1

Exp8 Kinetics of SN1 Solvolysis with tert-Butyl Chloride 2123-18 AR

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