What you need:
- vegetable oil
- food colouring
- effervescing (fizzy) aspirin or vitamin tablets
- a glass tumbler
What to do:
- Fill a glass tumbler about 1/3 full with water.
- Add a few drops of colourful food dye.
- Slowly pour vegetable oil into the glass so that it floats on the water, until the glass is almost full (tip-ping the glass a little helps it form a neat layer).
- Drop a tablet into the glass.
- Cue disco lights and music.
Safety note: Don’t dispose of the oil and water down the sink. Pour it into a container that can be sealed before putting it in the bin. Better yet, add it to your compost.
The bubbles in the water are carbon dioxide gas, formed when sodium bicarbonate and citric acid in the tablets react in the water:
acid + carbonate –> carbon dioxide + salt + water
C6H8O7 + 3NaHCO3 –> 3CO2 + Na3C6H5O7 + 3H2O
The bubbles take globs of coloured water with them up through the oil to the top of the glass. The gas bubbles burst at the surface and the coloured water drops then fall back down through the oil. You can recharge the lava lamp with another tablet when the first one has finished reacting.