DRAFT: This module has unpublished changes.

Introduction:

The goal of this lab is to develop and understanding of how the various intermolecular interactions affect the physical properties of substances and solutions. By heating separate solutions of Ethanol and Acetone, one can compare the relationship between the Hydrogen Bonds, and London-type Dispersion respectively, the strength of those bonds, and their effects upon the vapor pressure of the substance, the heat of vaporization of the substance, and the boiling point of the substance. This is done by graphing the natural log of the pressure, by inverse temperature, then from that graph, calculating the heat of vaporization via the Clausius-Clapeyron Equation:

The Clausius-Clapeyron Equation in its full form is used to show the mathematical relationship between the heat of vaporization and temperature:

The resulting differing heats of vaporization then demonstrate the weaker intermolecular interactions in Acetone, as compared to Ethanol. This is because stronger bonds require more energy to break, and thus require more energy to excite to the point of entering the gaseous state.

 

Equipment:

 

  • Data Collection System
  • Absolute Pressure Sensor with Quick Release, Connectors, and Plastic Tubing
  • Stainless Steel Temperature Sensor
  • Stand, with Clamp
  • Hot Plate
  • Graduated Cylinder, 25-mL
  • Graduated Cylinder, 250-mL
  • Erlenmeyer Flask, 250-mL
  • Beaker, 1500-mL
  • 100% Ethanol, 50 mL
  • Acetone, 50 mL
  • Electrical Tape
  • Mesh Pad, with Asbestos
  • Water, 1200 mL
  •  

     

    Method:

    • Gathered all equipment and materials. Inspected all equipment for damage or contamination.
    • Set up Data Collection System, assembled GLX, pressure sensor, associated tubing, with stopper, and temperature sensor.
    • Measured the volume of the Erlenmeyer flask, by filling it with water, then pouring the contents into the graduated cylinder. Dried flask.
    • Wrapped the Erlenmeyer flask with the electrical tape.
    • Covered with Stopper and associated tubing, then measured base atmospheric pressure.
    • Filled 1500-mL beaker with 1125 mL of water, and placed beneath stand. Placed temperature sensor in water bath.
    • Mounted the Erlenmeyer flask on the stand, ensuring that as much of it is immersed as possible within the bath.
    • Turned on Hot Plate, and waited until the water bath reached a temperature of 80ºC.
    • Measured 50.0 mL of Ethanol, and placed it in the Erlenmeyer flask.
    • Waited for the Ethanol to boil, and the Ethanol gas to fill the flask.
    • Removed flask from water bath, sealed flask, and placed on mesh pad.
    • Measured the shift in pressure as the temperature decreased, stopped measurements once the temperature reached 30ºC, then repeated the process with Acetone in place of Ethanol, and a water bath of 60ºC.
    • Disposed of solutions in designated containers. Cleaned all glassware, set them to dry in their designated areas, and returned all equipment to its point of origin.

     

    Data Analysis:

    The Heat of Vaporization of Ethanol is 158.7974, and Heat of Vaporization of Acetone is 0. This supports the prediction that Ethanol has stronger intermolecular forces than Acetone, due to its hydrogen bonds.

     

    Conclusion:

    The goal of this lab is to develop and understanding of how the various intermolecular interactions affect the physical properties of substances and solutions. By heating separate solutions of Ethanol and Acetone, one can compare the relationship between the Hydrogen Bonds, and London-type Dispersion respectively, the strength of those bonds, and their effects upon the vapor pressure of the substance, the heat of vaporization of the substance, and the boiling point of the substance. This is done by graphing the natural log of the pressure, by inverse temperature, then from that graph, calculating the heat of vaporization via the Clausius-Clapeyron Equation:

    The Clausius-Clapeyron Equation in its full form is used to show the mathematical relationship between the heat of vaporization and temperature:

    The resulting differing heats of vaporization then demonstrate the weaker intermolecular interactions in Acetone, as compared to Ethanol. This is because stronger bonds require more energy to break, and thus require more energy to excite to the point of entering the gaseous state.

     

    The Heat of Vaporization of Ethanol is 158.7974, and Heat of Vaporization of Acetone is 0. This supports the prediction that Ethanol has stronger intermolecular forces than Acetone, due to its hydrogen bonds.

     

    However, while these results support the prediction, they are also largely flawed. This is most likely due to a failure to properly seal the Erlenmeyer flask, thus allowing air to escape, disrupting the measurement of pressure. This is due to the two holes in the stopper, and the temperature sensor not properly fitting within the hole allotted to it.

     

    Other possible sources of error include:

    • Failure to properly attach to the pressure sensor's tubing, also introducing the possibility of leaks. 
    • Any defects with the GLX system or its sensors. Improper setup could also cause error.
    • Failure to properly measure the volume of the Erlenmeyer flask, thus disrupting subsequent calculations.
    • Failure to properly measure the volume, or concentration of the solutions.
    • Contamination of ethanol or acetone solutions.
    • Failure to properly maintain the temperature of the experiment, thus changing the pressure.
    • Failure to sufficiently heat the Ethanol or Acetone solutions, thus failing to fill the flask with fumes, thus removing or minimizing their effects on pressure, and disrupting all subsequent calculations.
    • Human error is always in effect, given that the laboratory does not function under ideal conditions. As such, there is always the possibility of inaccuracies with measurement, perception of measurement, inaccuracies of equipment, and other such errors. (However, this is not likely to be the sole cause of the inaccuracies within this experiment, though it may contribute to it.)

    Possible improvements that one could make to the experiment include using more accurate sensors, using containers that are less likely to leak, testing all measurements to ensure that they were performed properly, adding some means by which to test the seal of the Erlenmeyer flask, improving the fit of the temperature sensor to the stopper (thus resulting in a seal which is capable of holding pressure), ensuring that I and my lab partners read the experiment beforehand (increasing familiarity with the procedure, and minimizing human error), checking to see that all data has been properly distributed among all lab partners in a timely manner, and repeating the experiment multiple times (to minimize the impact of an anomalous result).

    DRAFT: This module has unpublished changes.