Methane bubbles demonstration

One of the most popular What’s In My Tray science demonstrations, Methane Bubbles, with help from Senior Science Technician Paul Cook and Science Technician Emilia Angelillo sharing two different techniques.

Learning outcomes

You will be able to:

• Describe the steps required to carry out the methane bubbles demonstration.
• Explain the chemical reaction that takes place during this combustion reaction.
• Cite an example of a fossil fuel that burns to give out energy.

You will need (per demonstration):

• 1 x Shallow Gratnells (F1) tray
• Sufficient warm water / 50ml washing up liquid or a self-prepared bubble mixture to half-fill the Gratnells tray.
• Methane gas source  (This must not be carried out using an LPG gas supply)
• Rubber tubing
• ~50ml washing up liquid
• 1 x Long splint
• 1 x 1m rule
• 1 x Tape
• 1 x Matches or safety gas lighter
• 1 x Lab Coat
• 1 x Safety Glasses
• Enough Heat proof mats to cover the work bench underneath the tray and area around it.
• Video recording equipment (optional)

Preparation:

• Check the ceiling in the area this will be carried out is free from flammable items.
• Check gas supply is methane gas – this must not be carried out with LPG gas supplies.
• Half fill the Gratnells tray with warm water.
• Tape the splint to the end of the meter rule.
• Put on your lab coat and safety glasses, tie back your hair if it is long.
• Set up your video recording equipment a safe distance from the demonstration.

What to do:

Ensure all spectators and recording equipment are a safe distance away (at least 3m away) from the demonstration area. This demonstration should only be carried out by a member of science staff who has practised it before carrying it out in a lesson or event.

• Add 50ml washing up liquid to the tray of water and stir gently.
• Connect the tubing to the gas tap and place the open end of the tube under the water in the tray.
• Open the gas tap and bubble the methane into the tray to create bubbles filled with methane gas.
• If lighting the tray of bubbles, then create only enough bubbles to be level with the top of the tray, resist the temptation to create a ‘mound’ of bubbles.
• Switch off the gas tap.
• If you wish to record the reactions, press start on your recording device now.

You now have two options:

1/ Push the sleeves up to your elbows and remove watches or jewellery/ bands if possible

Teachers/Science Staff must NOT perform this procedure on students (of any age), or visiting adults with no experience of such demonstrations. However, they may invite a responsible and known student to light the bubbles. Ensure the pile of bubbles is no more than 10 cm high. Ensure there are no bubbles ‘stuck’ underneath the hands.

Thoroughly wet your hands, scoop up a handful of methane filled bubbles (checking it is no more than 10cm high) and hold it at arms-length.

An assistant should light the long splint and, holding the meter rule at arms-length, ignite the bubbles in your hand.

If the methane bubbles begin to rise off your hand, light them as soon as they get into the air, and definitely while they are still a good distance from the ceiling.

or

2/ Light the long splint and, holding the meter rule at arms-length, ignite the bubbles in the tray.

Tip: You may wish to dim the lights to see the flames more easily.

Record your observations.

What is happening?

This is a combustion reaction. Methane burns in the presence of oxygen (from the air) producing carbon dioxide and water. The chemical reaction is:

CH₄ + O₂  → 2H₂O + CO₂

Methane is lighter than air, bubbles filled with the gas may rise into the air once released from the tray or may rise off your hands. When the bubbles light on fire, the bubbles are already moving up and off your skin and your hands will not get burned. Water is also a great conductor of heat, it pulls any heat away from your hand for the few seconds that the methane bubbles are on fire, hence the importance ensuring your hands are thoroughly wet before picking up the bubbles. As the flames heat the water on your hands, some of the water on the surface evaporates, this evaporation also creates a natural cooling process.

Other things to try…

• Make a model of methane and the products of its combustion using molymod® or another molecular model.
• What are the six major sources of atmospheric methane?
• How is methane used as a fuel?
• Share your flame test videos on social media using #WhatsInMyTray

Health & Safety

As with all Gratnells Learning Rooms What’s In My Tray Activities, you should carry out your own risk assessment prior to undertaking any of the activities or demonstrations. In particular, the most recent CLEAPSS guidelines on igniting floating bubbles filled with methane (SRA003) should be followed.