Water and Solubility
The water cycle
Water in the rivers, lakes and oceans of the Earth evaporates as the Sun supplies it with energy. The water vapour that forms rises into the atmosphere, where it cools and condenses to form the tiny water droplets that clouds are made from. As the clouds rise further they cool more and the water droplets get bigger. Eventually the droplets fall as rain, replenishing the water in the rivers, lakes and oceans. We call this constant cycling of water between the Earth and the atmosphere - sometimes passing through living organisms on the way - the water cycle.
Water and Solubility 2
Most gases are soluble in water to some extent, and so are most ionic compounds. But it is impossible to dissolve many covalent substances in water. In these substances there is little attraction between their molecules and water molecules.
We call the amount of a solute which we can dissolve in a certain amount of solvent the solubility of that substance. We usually measure the solubility of a solute in a solvent in grams of solute per 100 grams of solvent at a particular temperature. The solubility of most solid solutes increases as the temperature increases.
A saturated solution is one in which as much solute as possible has been dissolved. If we heat the solution, more solute will dissolve until the solution becomes saturated again. As a hot saturated solution cools down some of the solute will come out of the solution - it will crystallise out.