This week we're learning how to make lava lamps! These aren't your average lava lamps that need electricity to run. These lava lamps work using chemistry!

You will need:

• Clear 1 litre plastic bottle
• 150ml water
• Vegetable oil
• Food colouring
• Alka Seltzer tablets (or any effervescent tablet e.g. Berroca)

What to do:

1. Pour the water into the bottle.
2. Using a funnel, pour the oil in until the bottle is almost full.
3. Wait for the water and oil to separate.
4. Add 10 drops of food colouring to the bottle. The drops will pass through the oil and mix with the water below.
5. Break an Alka Seltzer tablet in half and drop it into the bottle. The tablet will sink to the bottom and start to dissolve.
6. For a true lave lamp effect, shine a torch through the bottom.

How does it work?

The oil stays above the water because oil is lighter, or less dense, than water. Water molecules and oil molecules do not like to mix. When the Alka Seltzer tablet begins to dissolve in the water, it produces bubbles of gas. This is because the Alka Seltzer contains sodium hydrogen carbonate and citric acid. When the tablet begins to dissolve, the sodium hydrogen carbonate and the citric acid react together to produce carbon dioxide gas. As the CO₂ gas bubbles rise through the water and into the oil, they carry some of the coloured water with them. When the blob of water reaches the top of the oil, the gas escapes and the water falls back down through the oil.

You can keep your lava lamp going by adding more tablets. The lava lamp can be stored with a lid on.

Don't forget to take some pictures of your lava lamps and send them into us to be in with a chance of winning some great prizes.

The School of Chemistry at NUI Galway advise that adult supervision is needed for all experiments. The portions of materials used in the experiments should not be increased from that described and mixtures prepared should not be ingested. The full text should be read before starting any experiment.

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