Hydrolysis of t-Butyl Chloride PDF

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Hydrolysis of t-Butyl Chloride lab report...

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Hydrolysis of t-Butyl Chloride

Charlene Mansour - Writer Catherine Burley - Reviewer Elisabeth Jones- Editor

Introduction Chemical kinetics studies the rates of reactions as well as the different factors that can affect these rates. When studying chemical kinetics, rate law of a reaction is often used. Reaction rate is the change in concentration of a substance vs. the change in time. The rate law formula expresses how changes in concentration affect the overall rate of a specific reaction. The formula for rate law is

When using this formula, the overall rate of the reaction is affected by the rate constant, k, as well as the concentrations of the substances involved in the reaction- which are indicated by the letters “A” and “B” in brackets. Furthermore, each substance in this rate law expression is raised to some reaction order- indicated by “a” and “b”- which express the degree to which the overall rate is impacted by the individual concentrations of substances. To determine the rate law, one must change the concentration of the substances involved in the reaction, and observe the effect that this change has on the overall reaction rate. If one changes a connotation and observes no change in the overall rate, the reaction is said to be “zero order” for that substance. If the rate changes linearly, the reaction is said to be first order. If the rate changes exponentially, the exponent for this reaction must be calculated. Ultimately, the overall reaction order is calculated by adding up all the individual reaction orders. Lasly, th ate constant (k) quantifies the relative reaction rate that is independent of concentration. There are several factors that impact the rate of reactions. These include: the concentration of each substance, temperature of the reaction, and use of a catalyst. As previously mentioned, the concentrations of each substance are included in the rate law. Catalysts increase the reaction rate by changing the rate law. They do this by allowing the reaction to go through a different reaction mechanism. Moreover, the effect of temperature on the overall reaction rate summarized in the rate constant (k), in the Arrhenius equation. Here, k1 and k2 are the rate contacts of the ration at temperatures t1 and t2. Ea is activation energy and R represents the ideal gas constant (0.008314 kJ/(mol*K).

Using this equation, the independent variable (x-axis) is 1/T and the dependent variable is ln(k). The slope of this plot is therefore equal to -Ea/R. THus, activation energy can be calculated by first determining the slop of the Arrhenius plot and multiplying the slope value by -R.

The purpose of this particular experiment was to investigate the effect of a change in concentration and temperature of the rate of hydrolysis of t-butyl chloride, as given by the following reaction:

The mechanism of this reaction involves the following steps:

In the first step, chloride leaves, forming a tertiary carbocation intermediate. In the second step, water acts as a base (nucleophile) and attacks the acid (electrophilic) carbocation. Finally, in the last step, a proton transfer occurs, with an additional water molecule removing a proton from the positively charged oxygen atom. As indicated in the image above, the first of these steps is the slow, rate-limiting step of the reaction. Table of Reagents Table 1- Table of Reagents Reagent

Weight g/mol)

Boiling point Melting point Density °C) °C) g/mL)

- butyl chloride

92. 57g

51

26

acetone

56

59.4

0.784

NaOH

1387.78

318

2.13

0.9

Bromophenol blue -butanol

195-196

3-7

2.2

83

25-26

0.781

Table 1 summarizes the reagents used this experiment.

Experimental

A room temperature water back was prepared in a large beaker, and the temperature of this bath was recorded. Using a 1mL graduated pipette, 3mL of a 0.10M t-butyl chlo chloride/acetone solution was pipetted into a dry, 25 mL Erlenmeyer flask. A dry 50 mL Erlenmeyer flask was obtained. Next, using a different 1 mL graduated pipette flask pipette 0.30 mL of 0.10 M NaOH solution was pipetted into the flask. Next, 6.7 mL of distilled water was measured using a graduated cylinder, and added to the flask. Then, 2-3 drops of bromophenol blue indicator were added and swirled: the solution appeared blue. The t-butyl chloride solution was quickly poured into the NaOH solution in the 50 mL flask. A timer was started the moment the solution was added. The flask was swirled and the solution was poured back into the 25 mL flask to ensure thorough mixing. The flask was then placed in the room temperature water bath to maintain a constant temperature until the indicator changed color, at which time the stopwatch was stopped. The following steps were repeated two more times, for a total of three trials. The same graduated pipettes were used for the solutions as in the first step. Additionally, before repeating, both flasks were rinsed with distilled water followed by acetone, and were left to air dry before the next trial. This entire process was repeated once more, but the following was added to the sodium hydroxide solution: 6.7 mL of distilled water, 2-3 drops bromophenol blue, and 10 mL of 70% water, 30% acetone. Then, two different large beakers with water were prepared to test the effect of temperature on the s For the first, the water was heated 10°C above room temperature. For the second, a cold water bath prepared by adding enough ice to the water to keep the mixture between 10-15°C. The solutions we Prepared in exactly the same manner as previously described. However, the only difference was tha mixing together, the flasks to sat in the desired water bath for 5 minutes, and after mixing, the 25 mL flask was kept in the water bath until the color change was observed.

Results Part A: Establishing a Baseline Trial Number

Time (sec)

Temp (°C)

1

68

23.9

2

59

26.7

3

80

26.7

Average

69

25.7

Trial Number

Time (sec)

Temp (°C)

1

90

24.5

2

100

24

3

129

23.6

Average

106.33 = ~106

24.0

Part B: Conc. Change

Part C: Temperature Dependence Hot Trial Number

Time (sec)

Temp (°C)

1

16.5

34.7

2

10.5

35

3

16.85

36.6

Average

14.62 = ~15

35.43

Trial Number

Time (sec)

Temp (°C)

1

289

21

2

275

21.5

3

302

20.8

Average

288.67 = ~289

21.1

Cold

Concentration Calculation Moles = concentration (M) x liters (L) t-butyl chloride: 0.1M x 0.003L = 3x10^-4 moles NaOH: 0.1M x 0.0003 L = 3x10^-5 moles

Calculation of Rate Constant (k): Part A: Trail 1: kt = 2.03 log(1/ 1-(10/100)) ; t= 69 k(68) = 2.303 log(1/ 1-(10/100)) k(68) = 2.303 log(0.046) k(68) = 0.105 k= 0.001544 k= 1.544x10^-3sec^-1 Trial 2: kt = 2.03 log(1/ 1-(10/100)) ; t= 69 k(59) = 2.303 log(1/ 1-(10/100)) k(59) = 2.303 log(0.046) k(59) = 0.105 k= 0.0017796 k= 1.780x10^-3sec^-1 Trial 3: kt = 2.03 log(1/ 1-(10/100)) ; t= 69 k(80) = 2.303 log(1/ 1-(10/100)) k(80) = 2.303 log(0.046) k(80) = 0.105 k= 0.001325 k= 1.3125x10^-3sec^-1 Average: kt = 2.03 log(1/ 1-(10/100)) ; t= 69 k(69) = 2.303 log(1/ 1-(10/100)) k(69) = 2.303 log(0.046) k(69) = 0.105 k= 0.001527

k= 1.527x10^-3sec^-1 Rate = 1.527x10^-3 x 0.1 = 1.527x10^-4sec^-1 Part B: kt = 2.03 log(1/ 1-(10/100)) ; t= 106 k(106) = 2.303 log(1/ 1-(10/100)) k(106) = 2.303 log(0.046) k(106) = 0.105 k= 0.00099 k= 9.9x10^-4sec^-1 Rate = 9.9x10^-4 sec^-1 x 0.1 = 9.9x10^-410^-5 sec^-1

Part C: Hot Trial 1: kt = 2.03 log(1/ 1-(10/100)) ; t= 16.5 k(16.5) = 2.303 log(1/ 1-(10/100)) k(16.5) = 2.303 log(0.046) k(16.5) = 0.105 k= 0.00633 k= 1.3125x10^-3sec^-1 Trial 2: kt = 2.03 log(1/ 1-(10/100)) ; t= 10.5 k(10.5) = 2.303 log(1/ 1-(10/100)) k(10.5) = 2.303 log(0.046) k(10.5) = 0.105 k= 0.01 k= 1.00^-2sec^-1 Trial 3: kt = 2.03 log(1/ 1-(10/100)) ; t= 69 k(16.85) = 2.303 log(1/ 1-(10/100)) k(16.85) = 2.303 log(0.046) k(16.85) = 0.105

k= 6.23^-3sec^-1 Average kt = 2.03 log(1/ 1-(10/100)) ; t= 15 k(15) = 2.303 log(1/ 1-(10/100)) k(15) = 2.303 log(0.046) k(15) = 0.105 k= 7x10^-3 sec^-1 Rate = 1.44x10^-3 x 0.1 = 1.44x10^-4 sec^-1 Part C Cold: Trial 1 kt = 2.03 log(1/ 1-(10/100)) ; t= 289 k(289) = 2.303 log(1/ 1-(10/100)) k(289) = 2.303 log(0.046) k(289) = 0.105 k= 3.63x10^-4 sec^-1

Trial 2 kt = 2.03 log(1/ 1-(10/100)) ; t= 275 k(275) = 2.303 log(1/ 1-(10/100)) k(275) = 2.303 log(0.046) k(275) = 0.105 k= 3.81x10^-4 sec^-1 Trial 3 kt = 2.03 log(1/ 1-(10/100)) ; t= 302 k(302) = 2.303 log(1/ 1-(10/100)) k(302) = 2.303 log(0.046) k(302) = 0.105 k= 3.37x10^-4 sec^-1 Average kt = 2.03 log(1/ 1-(10/100)) ; t= 289 k(289) = 2.303 log(1/ 1-(10/100))

k(289) = 2.303 log(0.046) k(289) = 0.105 k= 3.63x10^-4 sec^-1 Rate = 3.63x10^-4 x 0.1 = 1.44x10^-5 sec^-1

Fig 3.The Arrhenius plot was made from the k values of Part A, Part B, and from hot and cold tempe in Part C. The temperatures used were the average temperatures from each Part. The linear regression line shows a slope of -153. Activation Energy Calculation Ea = - Slope * R = - (-153K) * 0.008314 kJ/(mol*K) = 1.272 kJ/mol

Discussion As previously discussed, there are several factors that can affect the rate of a reaction. IN this experiment, it was proven that concentration is a factor that affects the rate of a reaction. This is due to the fact that increasing concentration also increased the number of particles, thus leasing to an increased number of collisions. As the concentration of the reaction decreases, the reaction slows down due to a decreased number of particles to collide with and thus a decreased number of collisions. In this particular experiment, the greater the concentration, the faster the reaction proceeded. The less the concentration, the slower the reaction proceeded. In this experiment, through part C, it was revealed that increasing the temperature also increases the rate of the reaction. This is the cause of molecules moving faster when at a higher temperature. This increased speed leads to more collisions as the reaction speeds up. However, when temperatures are lower, the opposite happens. The movement of molecules is slowed down and thus fewer collisions occur. This ultimately decreases the rate of the reaction. There are some potential parts of the experiment that are vulnerable to error. Common Errors. To begin, if one does not use different pipettes for NaOHand t-butyl chloride, the solutions can become contaminated. This will cause a premature reaction. Also, if one does not make sure to air dry flasks completely before each reaction, such wet flasks will cause a premature reaction. Premature reactions will not allow for the true duration of experiments and rate values to be calculated and will hinder the results of the experiment.

Conclusion In this experiment, the rate of the reaction of the hydrolysis of t-butyl chloride was investigates. Different variables were tested to see how they affected the overall rate of the reaction. It was concluded that the greater the temperature and concentration of the reactants, the faster the rate of the reaction. The lower the temperature and concentration, the slower the rate of the reaction. The overall aviation energy for the hydrolysis of t-butyl chloride was 1.272 kJ/mol. There are a few ways in which this experiment can be optimized. To begin, increasing the number of trials completed would give more accurate and precise results, including activation energy. Furthermore, the temperature varied for each trial in a certain Part. This could evidently lead to longer or slower rates of the trial, and thus inaccurate results. Thus, the temperature should be kept constant for each trial within a Part.

References 1. Libretexts. 6.2.3.1: Arrhenius Equation. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Te xtbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Ki netics/06:_Modeling_Reaction_Kinetics/6.02:_Temperature_Dependence_of_Re action_Rates/6.2.03:_The_Arrhenius_Law/6.2.3.01:_Arrhenius_Equation (accessed Nov 1, 2020). 2. Acetone | CH3-CO-CH3 - PubChem https://pubchem.ncbi.nlm.nih.gov/compound/ acetone (accessed Oct 21, 2016). 3. Bromophenol Blue https://pubchem.ncbi.nlm.nih.gov/compound/ 4. bromophenol_blue#section=experimental-properties (accessed Nov 1, 2020). 5. Hydrochloric acid | HCl - PubChem https://pubchem.ncbi.nlm.nih.gov/compound/ hydrochloric_acid (accessed Nov 1, 2020). 6. Sodium Hydroxide | NaOH - PubChem https://pubchem.ncbi.nlm.nih.gov/compound/ sodium_hydroxide (accessed Oct 21, 2016). 9. 2-Chloro-2-methylpropane | C4H9Cl - PubChem https://pubchem.ncbi.nlm.nih.gov/ compound/2-chloro-2-methylpropane (accessed Nov 1, 2020). 7. Water | H2O - PubChem https://pubchem.ncbi.nlm.nih.gov/compound/water (accessed Nov 1, 2020)....