In this demonstration, students will observe the combustion of a methane bubble. This exciting demonstration can be used as a dramatic and engaging introduction to the concepts of combustion reactions, chemical change, and balancing equations.
By the end of this demonstration, students should be able to:
- Write a balanced chemical equation for the combustion of methane.
This demonstration supports students’ understanding of:
- Chemical changes
- Balancing equations
Teacher Preparation: 10 minutes
Lesson: 10 minutes
- Dishwashing liquid, ~100 mL (Store brought bubble solution also works well)
- Glycerin, ~60 mL
- Water, distilled or deionized, ~700 mL
- Trough or large Pyrex glass bowl, ~1 L
- Borosilicate glass filter funnel, ~75 mm
- Tubing, rubber, ~10–20 ft
- Methane gas source
- Meter stick
- Masking Tape
- Candle, ~5 inches
- Wear safety goggles and chemical-resistant gloves at all times during demo.
- Only light bubbles when they are at least 3 feet above students’ and teacher’s heads and away from their faces.
- Do not light bubbles near any smoke detectors, sprinkler systems, etc.
- Shut off the gas source immediately after the bubble forms.
- An operational fire extinguisher should be in the classroom.
- Mix ~100 mL of dishwashing detergent, ~60 mL of glycerin, and ~700 mL of water directly in the trough or large Pyrex glass bowl and allow to sit for 24 hours. (Note: you can also purchase premade bubble solution).
- Connect the funnel to the gas source with the rubber tubing.
- Tape the candle to the meter stick and then light the candle. You may want a volunteer to hold the candle and stand off to the side while you turn on the gas to make the bubble. Instruct the volunteer to be careful to not let the melted wax drip on anyone as the candle burns.
- Turn on the gas valve on and adjust the flow to prevent the foaming from occurring when the funnel is dipped into the bubble solution.
- Dip the funnel into the bubble solution and hold the funnel upwards to allow a bubble to form. (Note: You may have to turn the funnel to one side of shake it in order for the bubble to dislodge – I found this part to be tricky because the bubble would burst before it even had a chance to dislodge. If this happens, you may need to turn down the gas valve so the gas comes out less quickly. Another way to prevent the bubbles from bursting is to coat the edges and the inner walls of the funnel with glycerin using a Q-tip before dipping it into the bubble solution).
- Turn off the gas as soon as the bubble has formed.
- DO NOT allow the bubble to grow to more than 4 or 5 inches in diameter. If it gets bigger than this, DO NOT attempt to light it.
- When the bubble is away from your face and above your head (at least 3 feet away from any person or flammable object), take the meter stick from your volunteer and place the candle flame next to the bubble (making sure that the flame touches the bubble). It may be helpful to have a fellow teacher/adult help with actually igniting the bubble with the candle.
- Have students observe the flame.
- Alternative title for the demo is the Dragon Ball Z demo.
- Students are expected to be familiar with combustion reactions and balancing equations for the analysis questions. If you use this demonstration as a hook at the beginning of a unit, you can come back to the student activity sheet after you have completed lessons on these topics.
- Once you have completed the demo, the excess soap solution may be stored for future use.
- If you are not comfortable performing this demo, you can use a video and discuss it with your students instead.
- For the final two analysis questions, if students are stumped, you can show this video, where someone wets their hands and holds the methane bubbles as they are set on fire and emerges unscathed. A video would be particularly helpful if you have not previously discussed the concept of specific heat or that water has a very high specific heat capacity, since this is addressed in the video.
For the Student
- What does the word combustion mean?
- What type of gas is methane and what is its chemical formula?
- What do you think will happen if we added fire/heat to methane gas?
- Why are the methane bubbles able to rise?
- What are the products for the complete combustion of all hydrocarbons?
- Write the balanced chemical equation for the combustion of methane.
- List three examples of hydrocarbons other than methane.
- What do you think would happen if you wet your hands and placed some of the methane bubble solution on your hands, then touched a burning candle to the bubbles?
- Why would your hand be unharmed by the flame?