Tuesday, June 24, 2008

Do oil and water mix?

What happens when an oil tanker spills oil into the ocean?

The oil floats on top of the water, causing environmental damage and killing fish and seabirds. Oil floats on water because it's less dense.

Oil and water don’t mix.

What you need:

four clear glasses, each half full of water
cooking oil
food colouring – red or blue show up best
liquid detergent

What to do:

Add a few drops of food colour to the first glass and stir. Notice how well the colour mixes with the water.
Pour some cooking oil into the second glass. Does it mix in like the food colour did? Try stirring the oil and observe what happens. The oil will eventually rise to form a layer on top of the water.
Pour enough cooking oil into the third glass to form a layer on top of the water approximately five centimetres thick. When the oil layer has settled, add a few drops of food colour. Don’t stir. Watch how each drop behaves as it hits the oil layer.
Now mix everything in together. What happens to the drops of colour? Some tiny drops of colour will probably stay in the oil layer. Watch what happens to them after a while.
Create the same oil and water mixture in the fourth glass, with several drops of food colour. Add a teaspoon of dishwashing detergent and stir vigorously. What is different this time? Notice the colour of the oil layer. Is it the same as the water layer?

What's happening:

Even when you stir them together, they will soon separate. The oil, which is lighter (or less dense), rises to the top. Food colouring is water-based, so it mixes easily with water, but can’t mix with the oil. Did you notice how the drops of food colour behaved when they travelled through the oil? Sometimes the food colour forms perfect little beads, which slowly drop through the oil layer.