An introduction to solvents and soluble and insoluble materials. Nail varnish is insoluble in water but will dissolve in a chemical called propanone or acetone. A liquid that will dissolve something is called a solvent.

A certain dye is shown not to dissolve in water, the most common solvent. No matter how much the dye is stirred into the water it will not mix at all. Ethanol is another example of a solvent. Dye is added to the chemical solution and it becomes coloured and clear. Clay will not dissolve in water - it is insoluble. It mixes with the water but the mixture stays cloudy.

First broadcast:
11 October 2007

This clip can help to introduce changing materials. After having shown the clip you could invite the children to conduct some experiments themselves and find out which materials are water-soluble or insoluble in water. Perhaps provide edible materials such as salt, sugar or flour. You could also provide liquids such as milk, vinegar or oil and ask the children to comment on their solubility in water. They could then try the solid materials in all the other liquids and draw up a table documenting their findings. You could maybe invite the children to think about how they could reverse the change - how could they get the salt and sugar back into a solid state?