Freezing Point Studies of Ethylene Glycol Solutions Freshman Chemistry

1
Freezing Point Studies of Ethylene Glycol
SolutionsFreshman Chemistry

• Christopher L. White,
• Paul E. Reinbold, Daryl G. Cox

2
In the Past..

• Freshman Chemistry students at SNU have been
  performing an analysis of an unknown mixture of
  ethylene glycol solutions using freezing point
  curves.
• The equipment used has changed twice since the
  introduction of this lab to the General Chemistry
  sequence three years ago. This work describes
  the use of Vernier Lab Pro devices along with
  laptop computers and the thermocouple probe
  (TCA-BTA) to acquire freezing point curves in a
  digital form.

3
Project Developments

• Initially, a digital thermistor probe was used to
  acquire the freezing point data in an isopropyl
  bath. This method caused some complications
• The Bath was not remaining in a slurry
• The thermister provided data inaccurate with the
  data obtained from the other methods used in the
  previous years.

4
Project Developments

• Instrumentation Change
• The thermocouple (TCA-BTA) was used. It provided
  data comparable with past data.
• Bath Composition Change
• The bath composition was changed to 90 ethanol
  and 10 isopropyl. This change corrected the
  problem of the bath freezing.
• By making the changes, the freezing point
  depressions were obtained, and the data acquired
  was accurate with the past data.

5
The Procedure

• To begin the analysis of the unknown mixtures of
  ethylene glycol, the freezing point curve of
  deionized water is first obtained and then the
  curve for the unknown. With the Vernier Lab Pro
  devices and software, both cooling curves are
  displayed in real time on the computer. Analysis
  of the two cooling curves then allows for the
  determination of the freezing point depression
  (?T).

Cooling curves on display
6
Acquiring the Data

• A mixture of ice and deionized water was used as
  the standard for the thermocouple. This provided
  a fairly consistent curve with which to analyze
  the unknown mixtures against.

7
Finding the EG of the Unknown

• Since it is known that the ?T is proportional to
  the molality (m?T/K), by knowing the molar mass
  of ethylene glycol to be 62.08 g/mol, simple
  calculations can be used to calculate the mass
  per kg of water.
• Using the equation below, students can calculate
  the EG in their unknown.

(w/w) EG mass EG x 100/ mass of solution
8
Data Analysis
The Vernier software allows for easy analysis of
the curves once they are obtained. Linear fits
make it simple to calculate the ?T.
?T8.13 m8.13/1.86 4.37m mass EG
(4.37m)(62.08g/mol) 271.29g/kg of water Total
mass of solution 1000 g H2O 271.29g
EG EG271.29/1271.29100 21.34 EG
9
Summer 2003 Data
10
Past Student Data
11
Conclusion

• The thermocouple worked well for the analysis of
  the EG/Water solutions.
• The new composition for the bath was sufficient.
• 30 solutions are not easily analyzed.
• It is suspected that the thermocouple does not
  provide linear results as the temperature change
  increases.
• Once the ?T reached between 17 and 19oC, the
  results were not accurate.

12
Lab Revision

• Because of the developments of this project, the
  lab procedure for General Chemistry is being
  revised. The various changes mentioned are being
  incorporated. At the end of this semester General
  Chemistry students will be able to use the
  laptops and Vernier devices to perform this
  experiment.

13
References

• SNU General Chemistry Lab Procedure, Freezing
  Point Depressions in Ethylene glycol-water
  mixtures.
• Experiments in Physical Chemistry, Shoemaker.
  McGraw Hill. New York, 1981.

14
Acknowledgements

• Southern Nazarene University, Department of
  Chemistry
• For the opportunity to perform this research
  project
• Dr. Paul E. Reinbold
• For the help and advice given throughout the
  project.
• Science Equipment Fund
• For helping fund the purchase of the new laptops
  and Vernier devices.