Boiling Point
–34.05°C
Boiling Point
–188.1°C
Boiling Points and Intermolecular Forces
A technician was cleaning up the laboratory when he discovered two
steel gas cylinders. One cylinder was labeled “Boiling Point: –
188.1°C”. The other cylinder was labeled “Boiling Point: – 34.05°C”.
Puzzled, the technician took the cylinders to his supervisor.
“One cylinder contains gaseous F2 and the other contains
gaseous Cl2” said his supervisor. She then asked the technician
to label the two containers correctly. He asked, “But, which is
which?” The supervisor responded indignantly “to a chemist,
that should be obvious!”
Seeing the disgruntled look on the technician’s face, she
offered the following hints to help him solve the problem.
The technician is you! Here are the hints:
Hint: Boiling points are related to intermolecular attractive forces.
1. a) List the three types of intermolecular forces.
___________________ ___________________ ___________________
b) Which one of these three forces is present in F2 and Cl2? ____________________
Hint: Molecular size affects the strength of intermolecular forces in the halogens.
2. Explain the effect that large molecular size has on the strength of intermolecular
forces. __________________________________________________________
3. Look at the periodic table. Can you decide which molecule is larger, F2 or Cl2? Explain
your answer. ______________________________________________________
________________________________________________________________
Hint: The strength of intermolecular forces in a substance determines its boiling point.
4. Do stronger intermolecular forces result in higher or lower boiling points? _________
5. Which substance, F2 or Cl2 has the stronger intermolecular forces? _____________
6. a) What is the boiling point of F2? _____________________
b) What is the boiling point of Cl2? ____________________
also see pages
424-426 for help.
