Purpose
To demonstrate the direct relationship between temperature and volume of a gas.
Materials
- Wide mouth, deep dewar filled partly with liquid nitrogen (hidden from view)
- Box of balloons (inflated to fit inside the dewar)
- Ignition tube with a lip (optional for advanced demonstration)
Procedure
- Preparation:
- Bring a wide mouth, deep dewar filled partly with liquid nitrogen to class without announcing its contents.
- Have a box of inflated balloons ready.
- Initial Demonstration:
- Explain to the students: “When studying gases, one of the easiest ways to visualize them is by using a balloon.”
- Inform students that you will place the balloons into the container and ask them to observe anything unusual.
- Observation:
- Start placing the balloons into the dewar.
- Encourage students to suggest why more balloons seem to fit than expected based on volume.
- Discussion:
- Ask students, “What must be happening to the balloon?”
- Students will likely suggest that the balloons are getting colder.
- Challenge their assumptions: “How do we know I’m not cheating and dissolving the balloons with acid or something? What happens if we take them back out?”
- Demonstration of Effects:
- Remove the balloons and allow them to warm up.
- Explain: “So what was in the container? Liquid nitrogen. This is very, VERY cold.”
- Demonstrate freezing a flower to illustrate the effects of low temperature.
- Concept Explanation:
- Discuss why the balloon collapsed: “The molecules inside slowed down at lower temperature. Remember, temperature is kinetic energy. When they slowed down, they couldn’t push on the sides of the balloon as hard, so the volume decreased.”
Advanced Demonstration (Optional)
- Oxygen Balloon:
- Use a balloon filled with oxygen attached by a rubber band to an ignition tube with a lip.
- Dip the ignition tube in liquid nitrogen.
- Observe that the balloon shrinks and blue liquid oxygen forms in the tube.
- Paramagnetism Demonstration:
- Pour the liquid oxygen between two poles of a magnet to showcase paramagnetism.
Conclusion
This experiment effectively illustrates Charles’s Law, showing the inverse relationship between the temperature and volume of a gas through direct observation and interactive discussion.