Impossible
to Mix

You can shake this one all day long—it will always return to its original three layers.

Duration 10 Min

Difficulty 2/4

Material list

What is happening

Normally, density columns are made by layering liquids of different densities. But if they disturbed or shaken all liquids get mixed up the soluble layers will combine and usually end up settling into two layers: a hydrophilic (polar) watery layer and a hydrophobic (nonpolar) oily layer.

If neighbouring layers are insoluble with each other, the column will stay in separate layers unless disturbed. To achieve this a special ingredient, “salt” is added to the mixture. It causes all three liquids to be insoluble with each other, you can mix the column as much as you like—it will always settle into three layers.

Directions

Gather the materials

You will need only a few things to do this experiment that can be found in your house.

Step 01

Add water to the bottle

Step 02

Pour vegetable oil

Step 03

Pour rubbing alcohol

Pour in a little more alcohol than the amount of water.

Step 04

Drop some food color and mix

Add few drops of food color you prefer. Let the mixture sit. How many layers do you see once the mixture settles?

Step 05

Let's separate the liquids

Add salt and mix until it dissolves. Keep adding and mixing until there is some salt that does not dissolve into the mixture.

Step 06

Shake the bottle and let it settle

Replace the cap. Shake the bottle so that everything mixes together and wait for it to settle. How many layers do you see once the mixture settles?

Step 07

More Science

The density column we made uses a phenomenon called “salting out” to preserve its layers. When salt is added to the mixture, the ions bond with the water molecules and exclude the slightly less polar alcohol molecules from forming hydrogen bonds with water, making it no longer soluble with water. The alcohol stays separate and ends up as its own layer on top of the column because it has a lower density than oil. Since the salt causes all three liquids to be insoluble with each other, you can mix the column as much as you like—it will always settle into three layers.