Magic Sand

What you need:

Magic sand
Ordinary sand (Hey ho it’s off to the beach we go!)
Teaspoon
Water
Small glasses
Washing up liquid

What you do:

Half fill each glass with water.
Add a couple of teaspoons of ordinary sand to the first glass.
Stir it up and bring a spoonful to the surface. It appears wet. The ordinary sand sinks to the bottom of the pot.
Add a couple of teaspoons of Magic Sand to the second glass.
Some of the Magic Sand sinks to the bottom of the pot. A small amount floats on the surface. Stir it up and bring a spoonful to the surface. It appears dry. The sand that has sunk appears silvery as if it has a coating around it.
See how the sand can be sculpted underwater to form different shapes?
Now add a few drops of washing up liquid to this glass. Stir it up. Can the Magic Sand be sculpted now? What has happened to the silvery layer? If you lift up a spoonful of the sand is it still dry? No it’s not!
Now look at what happens with vegetable oil.
Add two teaspoons of Magic Sand to another empty clean glass. Now add two teaspoons of vegetable oil. See how the vegetable oil soaks into the Magic Sand? Now you can lift out a spoonful of the sand and it no longer appears dry.

What’s going on?

Ordinary sand grains are hydrophilic (water-loving). This is because the surface of ordinary sand contains hydroxyl (OH) groups which are attracted to the OH groups in water molecules.

Magic Sand has been treated with a chemical called trimethylhydroxysilane. After this treatment the surface of the sand contains CH3 groups instead of OH groups. This makes the Magic Sand hydrophobic (water-hating). The Magic Sand repels water and so a layer of air is trapped around the Magic Sand as it sinks. This forms a bubble around the Magic Sand and the silvery layer is caused by the curved surface of the bubble.

Although Magic Sand hates water it loves oil (oleophilic) and so the vegetable oil is absorbed easily and the sand is ‘wet’.

Washing up liquid is a detergent which means that it contains molecules with both a water-hating and a water-loving end. When it is added to the Magic Sand in water it attaches to the water-hating groups on the surface of the sand. The water-loving end is attracted to the water molecules and so the Magic Sand is able to be wetted.

Magic Sand was originally developed as a way to trap oil spilled from oil tankers near the shore. It was developed by chemists at Cabot Corp. with the idea that it could be used to cleanse water of oily contamination. When sprinkled on an oil slick, magic sand attaches to the oil, adds weight, and sinks.

For more experiments with Magic Sand

Magic eh?