In this demonstration, students will observe how changing the temperature of a gas will affect the pressure of the gas through an engaging demonstration using a heat source, water vapor and a hard-boiled egg.
High, middle, and elementary school
By the end of this demonstration, students should be able to
- Recognize relationships between temperature, volume and pressure of a gas.
This demonstration supports students’ understanding of
- Gas Laws
Teacher Preparation: 5 minutes
Lesson: 10 minutes
- Water (~5ml)
- Hard-boiled egg, peeled
- Vegetable oil
- Bunsen burner
- Ring stand
- Ring clamp
- Wire mesh
- Erlenmeyer Flask – select a flask that has a neck that is slightly smaller than the peeled hard-boiled egg
- Heat resistant gloves
- Large beaker or bowl of water with a few ice cubes to cool it
- 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.
- 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 holding the egg in place while moving the flask.
- 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.
- Put a mixture of water and a few ice cubes into a large beaker or bowl.
- Place Bunsen burner on the ring stand. Attach the ring clamp so that it is a few inches above the top of the burner. Put wire mesh on the ring clamp.
- Add about 5 ml of water to the Erlenmeyer flask and rub a bit of vegetable oil around the rim and inner neck.
- Light the burner with the striker.
- Use the heat resistant gloves to put the flask on the wire mesh.
- Allow the water in the flask to heat and vaporize. You should be able to see water vapor filling up the flask.
- Turn off the burner and quickly put the egg into the opening of the flask. You will need to push slightly on the egg to keep it in place.
- With your other hand, use the heat resistant glove to remove the flask from the ring stand.
- Allow to cool for a minute and then put the bottom of the flask in the cool water.
- The sudden drop in temperature will condense the water vapor, reducing the pressure in the flask. Since the atmospheric pressure is greater than the pressure in the flask the egg will be drawn in.
- When the egg is completely in the flask remove the Bunsen burner from the ring stand and relight it.
- Using the heat resistant glove, invert the flask and shake it gently until the egg is stuck in the neck.
- Hold the flask at a 45 degree angle with the egg and neck pointing down and the bottom of the flask pointing up.
- Hold the base of the flask in the burner flame and gently heat the gas in the flask.
- The egg will slowly be pushed out of the flask as the gas pressure increases.
- Note: You can also use a hot plate to heat the water in the flask, but it takes a bit longer. Additionally, you cannot reheat the flask to push the egg out.