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Title: Exp. 1 : Kinetics of Nucleophilic Substitution Date: Tuesday, October 29 , 2024 Table 1: Potential Hazards for Experiment 1 Chemical / Apparatus Flammability Chemical Toxicity Mobility (Routes of Exposure) 2 - Chloro- 2 - methylpropane Highly flammable [1] Harmful if inhaled; can possibly cause dizziness and respiratory irritation [ 1 ] Inhalation, skin, and eye contact [ 1 ] Hydrochloric Acid (HCl) Non-flammable [ 2 ] Corrosive; can cause severe burns and respiratory damage [ 2 ] Inhalation, ingestion, skin, and eye contact [ 2 ] Acetone Highly flammable [ 3 ] Irritant; prolonged exposure can possibly lead to dizziness and drowsiness [ 3 ] Inhalation, skin, and eye contact [ 3 ] Water Non-flammable Generally safe; no significant toxicity No significant hazards
Balanced Equations of Chemical Reactions and Applicable Rate Laws:
- Balanced Chemical Reaction: The reaction is the hydrolysis of 2-chloro-2 methylpropane in water/acetone to produce t- butanol and hydrochloric acid: This reaction follows an SN1 mechanism where the formation of the carbocation is the rate- determining step.
- Rate Law for the Reaction: Since the hydrolysis of 2-chloro- 2 - methylpropane proceeds via an SN1 mechanism, it follows a first-order rate law with respect to the concentration of the alkyl halide, 2-chloro- 2 - methylpropane ((CH₃)₃CCl). The rate law can be expressed as: Where:
- Rate is the reaction rate (measured in moles per liter per second).
- k is the first-order rate constant (units: s⁻¹).
- [RX] is the concentration of 2-chloro- 2 - methylpropane.
- Integrated Rate Law Using Conductivity Measurements: To monitor the reaction progress, conductivity measurements are used to track the production of HCl, which increases the conductivity of the solution. The integrated rate law for a first- order reaction can be expressed in terms of conductivity as follows: Where:
- C∞ is the final conductivity value when the rxn reaches completion (plateau value).
- Ct is the conductivity at time t.
- C 0 is the initial conductivity (at t = 0 ).
- k is the rate constant.
Major Steps in the Experimental Procedure:
- Preparation:
- Dispense 10mL of 85/15 water/acetone solution into a 20mL vial with a variable-volume dispenser.
- Equilibrate solution to the reaction temperature on a stir plate and make sure of proper temperature stabilization.
- Calibration and Setup:
- Calibrate conductivity probe using 0μS and 10,000μS standards with LoggerPro.
- Set LoggerPro to collect data at 0.4 samples/second for a total of 450 seconds (Part A).
- Adjust parameters for Parts B and C as per temperature variation.
- Conduct Reaction Trials:
- Add volumes of 2-chloro- 2 - methylpropane (200μL, 400μL, 800μL) in sequential trials.
- Monitor and record conductivity data.
- Track the formation of HCl and corresponding reaction rate.
- Data Collection and Analysis:
- Save and export data as CSV files after each run for analysis in MS Excel.
- Perform linear regression on ln(C∞/(C∞ - Ci)) vs. time to calculate rate constants.
- Compare across different concentrations, solvent polarities, and temperatures.
- Cleanup:
- Rinse all glassware with distilled water.
- Dispose of reaction waste in organic solvent disposal can.
- Properly log off the computer to secure data files.
Works Cited:
- PubChem. "2-Chloro- 2 - methylpropane," National Center for Biotechnology Information, https://pubchem.ncbi.nlm.nih.gov/compound/2-Chloro- 2 - methylpropane
- PubChem. "Hydrochloric Acid," National Center for Biotechnology Information, https://pubchem.ncbi.nlm.nih.gov/compound/Hydrochloric-Acid
- PubChem. "Acetone," National Center for Biotechnology Information, https://pubchem.ncbi.nlm.nih.gov/compound/Acetone
- F. A. Carey. Organic Chemistry, 7th ed., Ch.8, pp. 318-342.
