Chm1046 Experiment 2: Intermolecular Forces

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Experiment 2: Intermolecular Forces
Performed: 9/12/2011
Submitted: 9/20/2011
Chemistry 1046L

The purpose of partI in this experiment is to identify a variety of unknown substances’ properties using observations of the temperature changes that occur during evaporation. We know that substances with weaker intermolecular forces, such as London dispersion, will have a faster vaporization rate and thus a higher temperature difference compared to those with stronger molecular bonds such as hydrogen and dipole-dipole forces. By measuring the average kinetic energy (or the temperature) of the liquid left behind after some evaporation takes place, we can determine its type of intermolecular forces and ultimately identify the unknown liquid when compared to other substances. Another purpose of part I of this experiment is to reiterate the use of web- based data and tables to organize our numerical results as well as deltaHvapand delta T calculations of substances. Also to teach the proper use and technique of laboratory materials such as the clamp apparatus, beaker, pipet and thermometer.

Unknown substance B had a mild scent of nail polish remover; Unknown E smelled similar to spray paint before and after probe soak and unknown D exhibited scent similar to rubbing alcohol. Unknown A, C had no smell. All five unknown were clear, colorless liquids. A: Table of Tem values (Tfinal-Tinitial) for the five unknown liquids (A-E) UnknownT initialT finalTf-Ti

A21.5 C8.8 C8.8-21.5 = -12.7
B18.0 C10.9 C10.9-18.0 = -7.1
C23.0 C18.0 C18.0-23.0 = -5.0
D23.5 C16.0 C16.0-23.5 = -7.5
E23.0 C10.0 C10.0-23.0 = -13.0

B: rankings of the unknown liquids from strongest (1) to weakest (5). Based on the T values found, the highest temperature decrease will have the weakest intermolecular forces and vice versa. 1.C

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