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Chemistry extended essay - investigate the effect of 2-bromo-2-methyl propane concentration and temperature of the system on the rate of reaction of solvolysis of 2-bromo-2-methyl propane in 90% ethyl alcohol

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Introduction

Chemistry Extended Essay To investigate the effect of 2-bromo-2-methyl propane concentration and temperature of the system on the rate of reaction of solvolysis of 2-bromo-2-methyl propane in 90% ethyl alcohol Done by: Habib Iscandar Hinn Friend's Boy's School June 22, 2007 To investigate the effect of 2-bromo-2-methyl propane concentration and temperature of the system on the rate of reaction of solvolysis of 2-bromo-2-methyl propane in 90% ethyl alcohol Introduction: The major product of the solvolysis of t -butyl chloride in 70 % water - 30 % acetone is t-butyl alcohol, with a small amount of isobutylene being formed as a by product And this is with accordance of first order kinetic and suggests a two step mechanism in which the rate determining step consists of the ionization of t-butyl chloride, and in this mechanism a carbonium ion is formed as inter- mediate and this bonds immediately to near by nucleophile (in this case nucleophile is a neutral molecule) the initial product is t-butyl carbonium ion. "Note1: if the nucleophile is neutral the product will be charged since the leaving group takes both bonding electrons away with it" So chemists have proposed to general types of mechanism: 1- Nucleophilic substitution Sn1 The ionization step in a Sn1 reaction is endothermic and much slower than the exothermic neutralization of carbonium ion by a nucleophile. And so the rate determining step being the unimolecular ionization of the t-butyl chloride equation 4, and as a result, the overall rate of reaction is not affected by changes in the concentration or kinds of nucleophilic reagents present. ...read more.

Middle

By finding the values of reaction rate constant K for different concentration of t-butyl chloride and different reaction temperature, we will find the effect of temperature on the solvolysis of t-butyl chloride in water acetone solvent. Quantitatively, K (s-1) is related to Ea and T by the equation K1 = Ae-Ea/RT1 ......1 Ea is the activation energy, in joule / mole. (Jmol-1) A is a proportionality constant, in s-1 R is the gas constant = 8.314 Jmol-1K-1 e is the base of the natural logarithms. T is temperature in Kelvin. This relation ship is known as Arrhenius equation We measure Ea by taking the natural logarithm of eq.1 Ln K = ln A - Ea RT Thus, a plot of ln k versus 1/T gives a straight line whose slope is equal to -Ea/R and whose intercept with coordinate is ln A "Note8: Ea is the activation energy, a constant characteristic of the reaction" We can calculate the rate constant at some specific temperature if Ea and K at some other temperature are known. For any temp. T1 (known), Ea (known), K1 (known) K1 = A e -Ea/RT1 For any other T2 (known); (K2 unknown) K2 = A e -Ea/RT2 By dividing K1 over K2 K1 = A e -Ea/RT1 K2 A e -Ea/RT2 Taking natural logarithm of both sides, we get Ln K1 = Ea (1/T2 - 1/T1). K2 R Or in common logarithms (base 10 logarithms) gives: Log K1 = Ea (1/T2 - 1/T1) K2 2.303 R And by finding the value of K2 we will be able to find the rate of reaction at T2 and we will find the effect ...read more.

Conclusion

in 70 % water - 30% acetone solvent at a temperature greater than room temperature by ten degrees. B, b, I:- 1- Prepare 500 ml of 0.1 M t- butyl chloride in acetone only and put it in an Erlenmeyer flask and label it #1. 2- Prepare 100 ml of 0.1 M NaOH solutions (in water) and put it in an Erlenmeyer flask and label it #2. 3- Using a burette take 30 ml of the solution in Erlenmeyer flask #1 and put it in an Erlenmeyer flask and label it #3. 4- By a graduated pipette put 3 ml of sodium hydroxide 0.1 M in an Erlenmeyer flask and label it #4. 5- Using a graduated cylinder measure 67 ml of distilled water added to Erlenmeyer flask #4. 7- Add two drops of bromo-phenol blue indicator to flask #4. B, b, II:- 1- Suspend the flasks #3 and #4 in a water bath full with ice and water, allowing the temperature of the flasks and their contents to equilibrate for ten minutes.(to reach the temperature of the water bath) 2- Adding quickly the solution in flask #4 to solution in flask #3 and start the stop watch to count for time in seconds. 3- Swirl the mixture and after one or two seconds immediately pour the combined solutions back into flask #4 to minimize the errors in the results. 4- The color of the mixed solutions is blue, so continue swirling the solution in flask #4 till the instant color of the solution start changing to yellow we stop the stopwatch and record the time 5- Repeat the procedure at least three times and calculate the average. 6- Tabulate the results in record B. ...read more.

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