Introduction
The term solubility refers to the maximum amount of material that will dissolve in a given amount of solvent at a given temperature to produce a stable solution.
Saturated and Unsaturated Solution
A saturated solution of a solute at a particular temperature is one which contains as much solute as it can dissolve at that temperature in the presence of undissolved solute particles.
A given volume of water can only dissolve a certain amount of salt in it at room temperature. If more salt is added to such a solution, the salt will remain undissolved. Such a salt solution is said to be saturated. On the other hand, an unsaturated solution can continue to dissolve more solutes, if added, until the solution becomes saturated. In a saturated solution, the dissolved solutes and the undissolved solutes are in equilibrium at a particular temperature.
Supersaturated Solution
A supersaturated solution is one which contains more of the solute than it can normally hold at that temperature. Supersaturated solution is unstable and the excess solute will separate out if the solution is disturbed slightly by shaking or even a dust particle is dropped into it.
Solubility Graphs or Curves
If the solubilities of a solute in a given solvent are plotted against their respective temperatures, a solubility graph or curve showing the effect of temperature on the solubility of the substance will be obtained.
By looking at the plot of solubilities below, you can see that most solids increase in solubility with an increase in temperature.
Gases, however, decrease in solubility with an increase in temperature.
Degrees of Saturation
When referring to solutions, there are three degrees of saturation—unsaturated, saturated, and supersaturated. If a solution is unsaturated, the solvent is capable of dissolving more solute. When the solution is saturated, the solvent has dissolved the maximum amount of solute that it can at the given temperature. At this point we say that the solution is in a state of dynamic equilibrium—the processes of dissolving and precipitation are happening at the same rate. A supersaturated solution is one in which the solvent contains more solute than it can theoretically hold at a given temperature. Supersaturated solutions are often formed by heating a solution and dissolving more solute, then cooling the solution down slowly. These solutions are unstable and crystallize readily…
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