In this demonstration, students will observe the impact of temperature change on a gas through an engaging demonstration using simple household materials.
Elementary and middle school
By the end of this demonstration, students should be able to
- Understand that oxygen is needed in order for a flame to sustain burning.
- Recognize relationships between temperature, volume and pressure of a gas.
This demonstration supports students’ understanding of
- Chemical Reactions
- Gas Laws
Teacher Preparation: 5 minutes
Lesson: 10 minutes
- water (~25ml)
- petri dish or small plate/saucer
- glass bottle, graduated cylinder, or glass cup
- candle (tea light works best or cut end from long stem candle)
- lighter or matches
- Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
- Always use caution around open flames. Keep flames away from flammable substances.
- Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
- Open flames can cause burns. Liquid wax is hot and can burn the skin.
- It is encouraged for the teacher to practice this before demonstrating it in their classroom. It may take a couple attempts in order to feel confident with the placement of the glass container.
- When practicing this demonstration, do not push the glass container onto the plate when covering the flame. Try to hold the container in the water surrounding the candle for best results.
- This is a quick demonstration, so you may want to do this multiple times in order for students to understand what is happening, and connect their observations to the content.
- Add water to the petri dish or plate. The water should be pretty shallow; the candle will float on top. Make sure the water isn’t filled completely to the edge of the dish/near overflowing.
- Place the tea light/candle on the water and light it.
- over the tea light/candle with the glass jar or substitute container.
- The candle will continue to burn for a few moments, and the air inside the container will increase in temperature. You may notice bubbles escaping from the jar into the surrounding water due to the increase in temperature, and pressure inside the jar. The gas molecules are moving faster due to the increase in temperature, pushing on the inside of the jar to increase the volume.
- When the candle has reacted with all of the oxygen inside of the jar, the flame will go out. The temperature will then begin to drop as the flame begins to dim, and so will the pressure of the gas. This decrease in temperature will cause the gas molecules to get closer together, along with the decreasing pressure, so the water will move into the jar to occupy the empty space. You will observe the candle and water rise in the jar during the temperature change!
- See the video for a full demonstration.
- For older students, this can be connected qualitatively or quantitatively to the gas laws.
- For young students it is best to let them watch the process happen first, and then repeat the demonstration while asking for input and interpreting the changes.