Evaporation
Salt particles move about the water. Each particle is surrounded by water molecules.
The water particles (molecules) keep the salt particles from rearranging themselves back into a salt crystal. Salt particles are carried throughout the solution surrounded by water particles.
As the water evaporates less and less water molecules are present to keep the salt particles apart. The salt therefore recrystalises and can be collected.
This is the way salt is collected from sea water. Sea water is trapped and allowed to evaporate leaving behind the solid salt.

1) a) Click to see an animation of water dissolving salt. Describe how the water molecules dissolve the salt crystal.

b) Why does the salt reappear when water evaporates?

2) What is the difference between a soluble and an insoluble substance?

3) Why can we not see the dissolved salt particles in the water but we can see the solid salt crystals?

4) Sugar is a soluble substance. Explain what happens to a cube of sugar as soon as it is placed in water.

5) Soluble nutrients can be absorbed by the roots of plants, through microscopic holes, where as insoluble nutrients can not. Explain why.