In this demo, students will observe the combustion of methane using hands-on practices.
By the end of this demo, students should be able to
- determine the chemical equation for the combustion of methane gas.
- write a balanced chemical equation for the reaction between methane and oxygen.
This lesson supports students’ understanding of
- Chemical changes
Teacher Preparation: 10 minutes
Lesson: 10 minutes
- Dishwashing liquid, ~100 mL (Store brought bubble solution also works well)
- Glycerin, ~15 mL
- Water, distilled or deionized, ~900 mL
- Trough or large Pyrex glass bowl, ~1 L
- 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 well above students’ heads and away from their faces.
- Do not light bubbles near any heat or smoke detectors.
- Shut off the gas source immediately after the bubble forms.
- Mix ~100 mL of dishwashing detergent, ~15 mL of glycerin, and ~900 mL of water directly in the trough or large Pyrex glass bowl. (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.
- 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. A tip 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).
- When the bubble is away from your face and above your head, place the candle flame next to the bubble (making sure that the flame touches the bubble).
- Have students observe the flame.
- Alternative title for the demo is the Dragon Ball Z demo.
Note: Question number 5 in the analysis can be a bonus demo for students. Make sure to wet your hand thoroughly with water before placing the methane bubble solution on it. Grab a handful of bubble solution and ask a student to light a match and touch the match to the bubble solution on your hand. Students will observe the flame formed. Try not to move hand around when the flame is formed.
For the Student
- What does the word combustion mean? (Answer: burning, ignition; in terms of a chemical reaction, combustion is a chemical process in which a substance reacts vigorously with oxygen to produce heat and light, seen as a flame)
- What type of gas is methane and what is its chemical formula? (Answer:
- hydrocarbon, CH4)
- What do you thing will happen if we added fire/heat to methane gas? (Answer: The methane will react with oxygen to form a flame)
Note: The answers to the questions can vary. The answer is acceptable if the student the key points or key terms.
- Why are the methane bubbles able to rise? (Answer: Methane gas is lighter than air)
- What are the products for the complete combustion of all hydrocarbons? (Answer: Carbon dioxide and water)
- Write the balanced chemical equation for the combustion of methane. (Answer: CH4 (g) + O2 (g) ⇾ CO2 (g) + H2O (l) ΔH = -864kJ/mole; methane reacts with oxygen to produce carbon dioxide, water, and heat)
- List three examples of a hydrocarbon other than methane. (Answer: Butane, propane, ethane, etc.)
- What do you think will happen if you placed some of the methane bubble solution on your hands and touched a burning candle to it? (Answer: You should see a flame form on the top of your hand; your hand will not get burned if it is wet with water because of water’s high heat capacity)
- Why is your hand unharmed by the flame? (Answer: Answer may vary, students should understand that water has a high heat capacity)