Solvolysis Reaction Lab Report

The purpose of this experiment was to observe how the change in solvent polarity affects the rate and to determine the kinetics of a solvolysis reaction. In this experiment, we used 1-chloro-1-phenylethane in acetone in one reaction with 50% ethanol-50% water and in another reaction with 40% ethanol-60% water. To monitor he rate of reaction, we would need the concentration of the alkyl chloride at the beginning of the reaction and at a time t, but since we did not determine the concentrations, we monitored the rate of formation of HCl since it would equal the rate of the disappearance of RCl. In order to measure the rate of formation, we used bromothymol blue as an indicator to measure the volume of NaOH needed to neutralize the solution.
Once it loses the chloride, a carbocation is formed and the water acts as the nucleophile to bond the oxygen to the carbocation.
Bromothymol blue indicator changes color depending on the pH of a solution. The indicator would change from blue to green to yellow. Using this indicator, we were able to measure the rate of formation of HCl by measuring the time in which the indicator turned blue to green and the amount of NaOH needed to turn it from green to blue again. The time and volume would then be used to obtain the rate constants. Bromothymol blue is a weak acid so it can be protonated and deprotonated causing it to appear yellow and blue.
For the first run with 50% ethanol-50% water, the k value was 0.0005s-1. For the second run with 40% ethanol-60% water, the k value was 0.0038s-1. The Rf value for the first run was 0.99 and for the second run it was 0.99, which tells us that the k value obtained is very accurate, almost exact. Based on these results, the amount of ethanol affects the formation of carbocation. The first run had a greater concentration of ethanol and it had the smallest rate constant, which means that the reaction was slower for the first run than the reaction for the second