Actually, the sun is aiding the evaporation of water in this reaction. When all the water has evaporated, only salt is left behind.
For a liquid to evaporate, it needs latent heat of vaporization. When the rays of sun strike the solution, they provide heat energy to it. This heat energy acts as the latent heat of vaporization and causes the water molecules to become excited.
Another thing that I should mention here is that in a liquid, the molecules are all pulled together by each other so that the net result is a liquid. When the forces of attraction are removed from between the molecules, the liquid (water in this case) becomes a gas (water vapor). Gases disperse because they have no forces of attraction between their molecules.
So, back to water, salt and sun:
The sun strikes the solution and causes the molecules to become excited. When a molecule has gained sufficient energy, it is able to escape/defy the force of attraction with the other water molecules and escapes the liquid as vapor. Eventually, when all vapors have evaporated, salt and water are said to have been completely separated.
Evaporation always happens on the surface of a liquid. Therefore, first the top layer of water molecules escapes and then progressively, the molecules below follow suit.
Some extra credit info: If you want to separate salt and water AND need both of them too, you can place a cool glass sheet on top of the container in which you have the salt and water mixture. Tilt the glass sheet slightly and place another container under it near the edge which tilts down. Water will condense on this glass sheet and collect in the container. Though this method is not used scientifically in a lab, you can do the following to keep the sheet cool: Simply place a bag of crushed ice on top of the glass sheet. Don't forget to replace the ice when it melts!
For a liquid to evaporate, it needs latent heat of vaporization. When the rays of sun strike the solution, they provide heat energy to it. This heat energy acts as the latent heat of vaporization and causes the water molecules to become excited.
Another thing that I should mention here is that in a liquid, the molecules are all pulled together by each other so that the net result is a liquid. When the forces of attraction are removed from between the molecules, the liquid (water in this case) becomes a gas (water vapor). Gases disperse because they have no forces of attraction between their molecules.
So, back to water, salt and sun:
The sun strikes the solution and causes the molecules to become excited. When a molecule has gained sufficient energy, it is able to escape/defy the force of attraction with the other water molecules and escapes the liquid as vapor. Eventually, when all vapors have evaporated, salt and water are said to have been completely separated.
Evaporation always happens on the surface of a liquid. Therefore, first the top layer of water molecules escapes and then progressively, the molecules below follow suit.
Some extra credit info: If you want to separate salt and water AND need both of them too, you can place a cool glass sheet on top of the container in which you have the salt and water mixture. Tilt the glass sheet slightly and place another container under it near the edge which tilts down. Water will condense on this glass sheet and collect in the container. Though this method is not used scientifically in a lab, you can do the following to keep the sheet cool: Simply place a bag of crushed ice on top of the glass sheet. Don't forget to replace the ice when it melts!
