Expt 005 -- Paramagnetic Oxygen Bubbles

Oxygen is a paramagnetic gas. This property is illustrated by pulling bubbles of oxygen about on the surface of water with a strong magnet.

Chemical Concepts

Substances with unpaired electrons are slightly attracted to a magnetic field. This is known as paramagnetism.

Background

• Paramagnetism is exploited by scientists to elucidate the electronic arrangements in molecules.
• Molecular orbital theory is a model used to describe the arrangement of electrons in molecules. One of its first triumphs was to explain the paramagnetic property of oxygen.

Safety

Use care in handling oxygen. Wear goggles.

Procedure

Preparation:

1. Fill a modified zipper plastic bag with oxygen. See Lab Hints.
2. In a large beaker, add 0.5 mL of Dawn^® dish detergent to 300 mL of water. Mix thoroughly.
3. Either use the tubing from the plastic bag to blow a bubble or fill a plastic pipet from your bag of oxygen and use the pipet to blow a bubble. To fill a pipet with oxygen, first squeeze air from the pipet. Open the pinch clamp and squeeze the bag slightly. Insert the pipet and fill. Remove the pipet; expel the first pipet full; and fill again. Do not expel air into the bag of oxygen. Try forming a single bubble of air about the size of a dime or nickel on the surface.

!!!Click here to See Movie.

Demonstration:

1. Place the petri dish on the overhead and pour in enough detergent solution to fill it completely -- then add a little more with a dropper so that the surface of the solution is domed slightly above the rim of the dish. Surface tension effects may interfere if the solution is not above the rim.
2. Blow a oxygen bubble about the size of a dime in the center. (Clusters of small bubbles exhibit strong surface tension effects which interfere. Skim off any clusters that form and try again.)
3. Set up wind-blocks around the petri dish (air currents can interfere with the demonstration). Bring the pole of the magnet near to the oxygen bubble and observe. Move the magnet slowly in one direction. Then move the magnet slowly in a different direction to show that the bubble is attracted to the magnet. Keep the bubble away from the edges of the dish where surface tension effects may interfere.

   The poles of the magnets shown are the large flat faces. Note the direction the magnets are held. Very strong magnets are required.

   !!!Click here to See Movie.

   Repeat the experiment with an air bubble to illustrate the difference between the gases.

   !!!Click here to See Movie.

Questions

1. Draw an energy level diagram for the oxygen molecule. Indicate the unpaired electrons which exhibit the paramagnetic behavior observed.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 005 Paramagnetic Oxygen Bubbles

Watch the movies.

1. Describe the movement of the oxygen bubble.
2. Answer the questions.

Curriculum-

This simple experiment can be used when discussing bonding. This demonstration is best for more advanced students.

Activity-

Laboratory or Demonstration

This activity works well as a demonstration for the overhead projector, but it could also be done individually by the students if a sufficient number of very strong magnets were available.

Safety-

Wear goggles and apron while collecting the oxygen in the plastic bag.

Time-

Teacher Preparation: 5 minutes

Class Time: 5 minutes

Materials-

• Oxygen from a tank
  • or
• Set up a station for collecting O₂.
• 200 mL of 3% H₂O₂ -- (Available from drug stores; use as delivered. Buy fresh.)
• 1 mL dry yeast or 5 mL of 0.1 M Fe(NO₃)₃ (50 mL--Dissolve 2.020 g of Fe(NO₃)₃¥9H₂O, ferric nitrate, Iron(III) nitrate in 27.5 mL of water and 2 mL* of 3 M HNO₃. Dilute to 50 mL with water.)
• 1 250-mL Erlenmeyer flask with one-holed rubber stopper to fit
• 1 3-cm length of glass tubing
• 1 3-cm length of rubber tubing
• 1 pinch clamp
• 1 #4 one-hole rubber stopper
• electrician's tape
• 1 1-pt. zipper plastic bag
• a petri dish
• a VERY strong magnet (e.g., neodymium -- available from Micromole Scientific)

Disposal-

All of these chemicals used in this experiment may be disposed of safely at the sink.

Lab Hints-

• Before class, prepare a beaker of detergent solution and practice making air bubbles about the size of a dime. Adjust detergent if necessary. Detergents vary in concentration and components.
• Make a plastic bag storage tank: cut 1-cm off the bottom corner of a zipper plastic bag, open the bag and wedge the #4 stopper into the hole in the corner. Wrap some electrician's tape tightly around the bag and stopper to make an air tight seal. Insert a short glass tube half-way into the stopper, then place a short length of rubber hose over the glass tubing. Expel the air from the bag, then use a pinch clamp to close off the hose.

Obtaining Oxygen in the modified plastic bag

1. Fill a plastic bag storage tank with oxygen from a cylinder (try the shop) or from a simple generator.
2. Place 200 mL of 3% hydrogen peroxide in the 250-mL Erlenmeyer flask, add the 1 mL of granular yeast (or 5 mL of 0.1 M Fe(NO₃)₃), cover with a one holed stopper (fitted with a short glass tube). Allow the reaction to run 30-40 seconds to flush out any air in the flask, then connect the hose of the plastic bag to the glass tube of the generator, and immediately open the pinch clamp.

   !!!Click here to See Picture.

3. When the bag is half-filled, remove it from the generator, squeeze it empty and place it right back on the generator. This flushing out procedure ensures a relatively pure sample of oxygen in the bag. When the bag is almost full close the pinch clamp and remove the bag from the generator.

Observations-

The bubble is pulled about on the surface of the detergent solution. The oxygen bubble is more paramagnetic than the surrounding air which is only 20% oxygen. Bubbles of air are not attracted by the magnet because there is no differential between the bubbles and the surrounding gas.

Answers-

Q1. Draw an energy level diagram for the oxygen molecule. Indicate the unpaired electrons which exhibit the paramagnetic behavior observed.

A1. Note unpaired e^-s

Key Words 1-

paramagnetic, unpaired electrons, molecular orbitals, magnetic fields