Fami
Homemade lava lamp
Red water bubbles rising and sinking through oil.
Materials
- 1Tall glass
- 80 mlWater
- 240 mlSunflower oilor Olive oil, Baby oil
- 10 dropsRed food colouringor Food colouring of any colour, Watered-down poster paint
- ½Effervescent tabletor 1 teaspoon of coarse salt (shorter effect)
- 1Dinner plate
Step by step
- 1
Pour 80 ml of water into the tall glass
About a quarter of the way up
- 2
Add 240 ml of oil
Pour it slowly: it sits on top of the water
- 3
Add 10 drops of colouring
They sink through the oil and colour the water
- 4
Drop in half an effervescent tablet
And watch what happens in the oil
Result
Lava lamp!
Why does it happen?
Oil is lighter than water and they don't mix, so it floats on top. The tablet releases gas that rises, dragging up bubbles of red water; at the top the gas escapes and the water sinks back down.
For parents
The science, so you can answer
Oil and water do not mix and oil is lighter, so it floats; the gas from the tablet lifts the water up and lets it fall.
Water particles attract each other strongly and keep oil particles out, so they never mix. Oil is less dense (a glass of oil weighs less than the same glass of water) and stays on top. Food colouring dissolves in water, not in oil, so it only colours the water. The effervescent tablet contains an acid and baking soda that react when wet and release gas; the bubbles carry blobs of red water upwards, the gas escapes at the surface and the blob, heavier than oil, sinks back down.
What they will ask you
«Why does the oil stay on top?»
Because it weighs less than water for the same amount. What is lighter floats on what is heavier.
«Why don't they mix even if I stir?»
They break into drops, but soon each joins its own kind again: water with water and oil with oil.
«Why do the blobs go up and then come down?»
They ride up on a gas bubble. At the top the bubble pops, the water loses its float and sinks because it is heavier than oil.
«Why does it stop?»
The tablet is used up. Drop in another piece and it starts again.
In real life: That is why oil spills float on the sea, and why salad dressing separates in the bottle if you don't shake it.
Animated step by step
Follow it with your phone on the table: it pauses at the end of each step.