Oil and water do not mix.
Place drops of water-based food colors into oil, they form balls which sink into the oil. If the balls of food coloring contact a sugar cube, they will wet the sugar cube.
Put enough oil into the cup to completely cover a sugar cube.
To Do and Notice
Drop a sugar cube into the oil.
Notice that the oil penetrates the sugar cube driving out a steady stream of small bubbles.
The cube remains a cube and does not crumble or dissolve in the oil.
Put a drop of food coloring into the oil, make sure the first drop misses the sugar cube.
Notice that it forms a colorful ball which sinks into the oil.
Put another drop of food coloring into the oil so that it lands on top of the sugar cube.
Notice that the colorful ball settles on top of the sugar cube then spreads out over the surface and penetrates into the cube.
Add more drops in different colors.
For comparison you can drop a sugar cube into water. It will crumble and dissolve.
What's Going On?
The food coloring is dissolved in water and glycerin which do not mix with oil. Water and glycerin are polar solvents, they have electrical charge distributions which give them a positive side and a negative side. In water the hydrogens become positive while the oxygen becomes negative. Polar solvents dissolve polar or charged materials easily, for example salt and sugar. Oil is non-polar. Non-polar molecules dissolve more easily in non-polar solvents. Baby oil will completely dissolve in cooking oil. Polar sugar does not dissolve much in non-polar oil. However, drops of colored water wet the sugar and dissolve the sugar.
If you can find some oil-based food coloring such as Easter egg dyes or candle dyes observe what happens when you place drops of the oil based coloring into the cooking oil. The oil based dyes will spread throughout the oil.
There are oil based paints and water based paints. These paints will not mix.
Other non-polar liquids include kerosene, mineral oil, and butter.
Polar liquids include alcohol and vinegar.
Salad dressing is a combination of oil and vinegar. Before it is used the salad dressing is shaken to disperse drops of each liquid throughout the other.
Milk is a mixture of fat in water, homogenized milk is forced through a nozzle under high pressure, this breaks up the milk fat into such small drops that they drops will not separate from the water. The drops form a suspension.
In the core and mantle of the earth molten metals and molten rock do not mix.
Scientific Explorations with Paul Doherty
18 August 2005