Oily hubbub
Watch this mini lava lamp effect. So simple yet so engrossing…
You will need:
- A clear glass jar or other container
- Vegetable oil
- Water
- Food colouring (if you like)
- Salt
What to do:
- Pour water into the jar to about 10 cm depth.
- Add 2cm of oil. When it has settled see if the oil and water have mixed. Is the oil on top of or underneath the water?
- If you like, add a little drop of food colouring into the jar as well and see what happens to the drop.
- Sprinkle salt on top of the oil and watch carefully. What happens to the food colouring and what happens to the salt?
- You can add more salt to keep the action going.
What’s going on?
The oil and the water don’t mix – they are immiscible – and the oil is less dense than the water, so when you add oil to the jar it just sits in a layer on top of the water.
The food colouring just sits there, too, until you add the salt…
The salt is insoluble in the oil – this means it doesn’t dissolve. It is also more dense than the oil. Gravity pulls the salt down to the bottom of the glass, and the salt drags some of the oil with it in little blobs.
When the salt reaches the water it starts to dissolve, and the blobs of oil rise up to join the layer on the top again.
Once all the salt you’ve added has dissolved, the mixture calms down – until you add more.
This activity came from Planet Science’s Little Book of Experiments.
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