Molecular Structure, Bonding, Orbital Hybridization
9.2 Properties of Liquid Oxygen
Subjects: Atomic structure, periodic trends
Description: Liquid oxygen is produced by the condensation of oxygen gas onto a metal coffee can full of liquid nitrogen, and then collected into a styrofoam cup. The blue color of liquid oxygen is observed and the magnetic properties demonstrated.
Materials:
- Metal coffee can
- Dewar* of liquid nitrogen◊
- Ring stand with clamped ring
- Styrofoam coffee cup
- Ring magnets tied to a string
- Optional: Vernier Thermocouple, Interface, and Logger-Pro or Logger-Lite software.
*Shared Item. Located on the shelves in the alcove. Vernier items are located in the drawers opposite the bin storage shelves..
◊Requires advanced preparation. Get LN2 ahead of time.
Procedure:
- Support the coffee can on the ring so that it is at an angle and the bottom edge of the can is pointing down (see photo).
- Set the styrofoam cup under the edge of the can to catch the condensing liquid oxygen.
- Pour the liquid nitrogen into the coffee can.
- Liquid oxygen (LOX) will condense on the surface of the can and drip into the cup beneath.
- When enough LOX has been collected, allow the students to observe the blue color.
- Dip the magnets into the liquid oxygen and remove, pulling out some of the liquid oxygen that is clinging to the magnets.
Discussion:
Oxygen gas condenses to a liquid at -183˚C. Liquid oxygen is paramagnetic. A paramagnetic element or compound has unpaired electrons that align when a magnetic field is imposed. Molecular orbital theory predicts a configuration with a bond order of 2 and two unpaired electrons, in agreement with experimental results.
Safety:
Liquid oxygen and the liquid nitrogen in which it is immersed in the Dewar flask are extremely cold. Wear insulating gloves to prevent skin exposure. Liquid oxygen is a very powerful oxidizer. Make sure that this demonstration is performed away from sources of combustion.
References:
1. J. Kotz, P. Treichel, J. Townsend; Chemistry & Chemical Reactivity. 7th Ed. Instructor’s Edition; Brooks/Cole; 2009