Introduction

     The purpose of this lab is to determine how intermolecular interactions affect physical properties.  There are three different fundamental interactions all known as the van der Waals interactions. They are dipole-dipole, ion-dipole and london type dispersion forces. Dipole-dipole interactions are between two dipole molecules. A special type of dipole-dipole interactions is the hydrogen bond which exists between a partially negatively charge atom, such as oxygen or nitrogen, and a hydrogen atom attached to a high electronegativity atom. Hydrogen bonds are strong bonds. Ion-dipole forces are between ions and polar molecules. London dispersion forces are weak and are based on temporary induced polarity between two nonpolar molecules. Stronger bonds have a higher melting point and boiling point and lower vapor pressure. Stronger bonds have larger molecules.

      In this lab the molecules being tested are ethanol and acetone molecules. In this lab the pressure will be found in a 250 mL Erlenmeyer flask at 80 degrees Celsius. Then 50 mL of ethanol will be heated on the hot plate in the 250 mL Erlenmeyer flask that is in a water bath until the ethanol starts to boil. This will give the boiling point of ethanol. Then the flask should be removed from the hotplate immediately and wait until the temperature drops to about 30 degrees Celsius. The same thing should be done for 50 mL of acetone in a 60 degree water bath and then allowing the acetone to cool to about 25 degrees Celsius.

            Once the boiling and melting points of the acetone and ethanol are found, the Clausius-Clapeyron equation that relates heat vaporization and temperature can be applied to determine the heat of vaporization. The heat of vaporization is the energy required for a known amount of substance to escape from the liquid to gas phase. The equation is   P is the vapor pressure of the substance,  is the change of heat of vaporization, t is the temperature, C is a constant and R is the gas constant. Acetone has weak bond strength and has London Dispersion forces. Ethanol has strong hydrogen bonds. Ethanol is lighter and has a higher boiling point than acetone because of the hydrogen bonds in the ethanol molecules. So the expected results will be that ethanol will have a higher heat of vaporization than acetone.