Explain how it works
The oil floats on top of the water because it is less dense or lighter than water. The food colouring has the same density as the water so it sink through the oil and mixes with the water. When you add the tablet it sinks to the bottom then starts to dissolve. As it dissolves it makes gas, carbon dioxide. Gas or air, is lighter than water so it floats to the top. The air bubbles bring some coloured water with them to the top.
Follow up questions
- When it stops bubbling, try sprinkling some salt into your lava lamp. What happens?
- What happens if you put the cap on after dropping the fizzy tablet in?