types of solutions

You may be asking yourself why solutions are necessary. Well, they serve a lot of practical purposes. For instance, most chemical reactions are run in solution. Solutions also usually have a lower melting and freezing point than just a substance by itself.

Let's say that we have a handful of salt crystals, NaCl. When this salt dissolves in water, there is a uniform dispersion of ions in this water. What we have just formed is called a solution. A solution is defined as a homogeneous mixture of two or more substances, consisting of ions or molecules. A solution can be a solid, liquid, or gas. A solution results from the combination of a solute and a solvent. A solute is, in the case of a gas or solid dissolved in liquid, the gas or solid, but in other cases it is the part that has the smaller amount. A solvent is, in the case of a gas or solid dissolved in liquid, the liquid, but in other cases it is the part that has the larger amount. In the example concerning the salt, the solvent would be water and the salt would be the solute.

So that we can understand the concept of solubility, let's consider the process of dissolving sodium chloride in water. We know that NaCl is an ionic compound, and that it dissolves in water as Na⁺ and Cl^- ions. When we mix 50 grams of salt in 100 mL of water we find something cool going on. The sodium and chloride ions leave the surface of the crystal and enter into the solution. These ions then move about at random in the solution and occasionally bump into another crystal and stick, returning to their crystalline state. As time passes, more sodium chloride continues to dissolve into the solution, which means that the ion concentration increases. This means that eventually more ions are going to bump into each other and return to their crystalline state. Over time, a dynamic equilibrium will be reached in which the rate at which ions leave the crystals is equivalent to the rate at which ions collide to form a crystal.

At this equilibrium, no more salt appears to dissolve. We have reached what we call a saturated solution. A saturated solution is a solution that is in equilibrium with respect to a given dissolved substance. An unsaturated solution is a solution that is not in equilibrium with respect to given dissolved substance, leaving room for more substance to dissolve. The solubility of a substance is the amount that dissolves in a given quantity of water at a given temperature to give a saturated solution. Sometimes, through special circumstances we can obtain a supersaturated solution. A supersaturated solution is a solution that contains more dissolved solute than is normally possible at that temperature.