Chem 222 Lab 5 Report

1362 words 6 pages
IMF: Evaporative Cooling and Molecular Modeling
ChemInquiry 5

Experiment Completed on Tuesday, October 21, 2014
Report turned in on Tuesday, November 3, 2014

Author: Katyna Omidfar-Tran
Partner: Jesus Palomo
Data Analysis Questions
1. Molecular Series I, II, and III all have London Dispersion forces, Dipole-Dipole moment forces, and Hydrogen Bonding forces.
2. Molecular Series IV all have London Dispersion forces only
3. In Molecular Series I (Straight-Chain Alcohols): As you go through the group from methanol  ethanol  1-propanol  1-butanol:
A. The IMFs that are changing in Molecular Series I are London Dispersion forces.
B. Claim: As we go from methanol  ethanol  1-propanol  1-butanol the dispersion forces increase.
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The dipole moment is correlated to the strength of the intermolecular forces, with a larger dipole moment correlating to strong IMFs, and visa versa. The steric hindrance is also correlated to the strength of the intermolecular forces, with the larger presence of steric hindrance correlating to weak IMFs. Additionally, as can also be seen in Table 4 on page 3A of the Appendix, shows that the ΔT decreases in the order of 1-butanol  sec-butanol  1-ter-butanol. The ΔT is correlated to the strength of the intermolecular forces, with a large negative ΔT correlating to weak IMFs, and smaller negative ΔT correlating to strong IMFs.
D. Hypothesis: I propose that the reasons the IMFs (specifically hydrogen bonding) decrease from 1-butanol  sec-butanol  1-ter-butanol are that a decrease in the surface area and decrease in dipole moment in the molecule decrease the strength of the hydrogen bond IMFs.
An increasingly negative ΔT is a reflection of the weakening dispersion forces because in a sample of molecules, a weaker IMF (dispersion forces) will require a lower kinetic energy for the molecule to break free of the liquid and become part of the vapor. The more molecules that are able to escape into the vapor, the greater the decrease in temperature due to evaporative cooling. Thus, a larger negative ΔT corresponds to a substance in which the IMFs