from Exploratorium
Have you ever seen a lava lamp? Two different coloured liquids swirl together in constantly changing ways. Now you can make you very own!
A clear jar or drinking glass
Water
Vegetable oil
Food colouring
Salt
from Exploratorium
Adult supervision is recommended. Carefully fill the jar with several inches of water. Add a slightly smaller amount of oil to the jar. Which settles on top? Add several drops of food colouring. What happens?
Sprinkle salt onto the surface of the liquid as you count slowly to five. Cool! Keep adding salt to continue to effects.
Oil and water have different densities. This means that one is heavier than the other is. Since the water in on the bottom and the oil is on the top, water is the more dense liquid. Oil and water do not mix because they have different chemical properties that act to repel each other rather than to attract. When you add salt to the surface, it combines with the oil layer to make the oil heavier. This causes the oil to sink into the water layer. Salt is very soluble in water, which means that is easily dissolves out of the oil into the water. When this happens, the oil becomes lighter again and returns to the surface of the water. This can happen over and over again until the water becomes saturated with salt and it no longer able to dissolve the salt. But salt is very soluble in water and it takes a lot of salt to completely saturate water. So you are guaranteed lots of fun!