Frozen Balloons

Objectives

• Describe the properties of gases and liquids.

• Understand the transitions between states of matter.

• Describe different properties of matter.

Materials

• Per Demo or Class:
  long balloons
  tall vacuum container/dewar containing liquid nitrogen
  a table to perform the demonstration, placed at a safe distance in the room
  gloves for protection
  goggles for protection
  tongs

Key Questions

• What is the name for the transition occurring inside the balloon?
• Why is there liquid inside the balloon after you put the balloon into the liquid nitrogen?
• Why does the liquid inside the balloon change back into a gas when the balloon comes into contact with the room temperature air or the table?

What To Do

Preparation:

1. Review the demonstration before attempting it in the classroom. Watch this video to review the key steps.

Safety notes:

• Make sure the students understand that liquid nitrogen will hurt if they come in contact with it.
• Remind students about safety while working with liquid nitrogen and tell them to not try this demonstration at home.
• Liquid nitrogen should never be placed in a container with a sealable lid. Vaporization of the nitrogen could cause the container to build up a lot of pressure and explode.

Demonstration:

1. Set up the liquid nitrogen and balloon on a table and make sure the students are at a safe distance away, but are still able to watch the demonstration.
2. Review safety precautions once again before the demonstration.
3. Blow up a balloon and tie it up making sure there are no leaks.
4. Put on safety goggles and gloves before handling the liquid nitrogen.
5. Open up the container with the liquid nitrogen and slowly place the balloon into the container with the tongs.
6. Make sure the balloon has completely contracted before taking it out.
7. Show the students the balloon. It has a liquid inside it. This is liquid air (mixture of oxygen and nitrogen). What happened to the gas? Discuss and explain what happened to the gas as a group.
8. Ask the students to predict what will happen when the balloon is placed onto a table. Discuss some possible predictions. You may want to describe what should happen before the balloon is placed on the table. It should start expanding because the table’s temperature will be much higher than the boiling point of liquid air.
9. Now, place the balloon onto a table. What is happening? As you all observe the balloon, have students take note of the disappearing liquid and the expansion of the balloon. The liquid air absorbs the heat and turns back into a gas.

Other Resources

Science World | YouTube | A Moment of Science: Liquid Nitrogen