Experiment 2: Boiling Points
o Date experiment was performed: September 16, 2011
o Objective: To determine the boiling point of organic compounds such as tert-butyl alcohol, sec-butyl alcohol, n-butyl alcohol, and an unknown.
o Principle: Boiling point is the temperature at which gas and liquid phases coexist in equilibrium. At this temperature, the vaporization rate and the condensation rate are equal. The liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate.
The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. While a gas is forming, the vapor pressure within the gas bubbles equals the external pressure. However, if the vapor pressure does not equal the external pressure, the bubble may burst or corrupt. If the vapor pressure within a bubble is lower than the external pressure, the bubble will corrupt. If the inverse is true, the bubble will burst. Maintaining an equilibrium pressure between vapor pressure and external pressure allows the boiling point to be maintained at a constant temperature. However, vapor pressure and the external pressure vary slightly so the boiling point temperature will vary slightly as well. Due to the variations in pressure, the temperature observed during boiling is taken to be an average value.
At this equilibrium temperature the heat added to the system goes into pulling the molecules further apart from each other. The strength of the attraction forces that hold a liquid together such as dispersion forces tends to increase with increased molecular weight. This is due to the fact that larger atoms have larger electron clouds which are easier to polarize. Polarization also increases the boiling temperature because polarity creates strong attractive forces within the molecules of the substance, requiring more energy to break those bonds.... [continues]
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