We set out to make a lava lamp.
We know that oil and water don't mix.
We thought that oil might float on top of water so we checked this out.
Next we added just a few drops of food colour.
The food colour stayed in little droplets in the oil (because the water in the food colour doesn't mix with the oil around it). When we shook the bottle the drops of food colour dropped underneath the oil, and when they came in contact with the water the food colour mixed with the water. (The droplets disappeared and the colour spread out into the water.)
When we added a fizzy tablet a chemical reaction took place......the tablet reacted with the water and made a gas (carbon dioxide). This gas rose up to the top of the water and oil, taking bubbles of colour with it. It looked exactly like a lava lamp and lasted as long as the tablet kept reacting with the water.