Solubility & Saturation
Solubility - The amount of a solute that will
dissolve in a specific solvent. A
substance may dissolve in a solvent, and it may not. For instance, salt dissolves easily in
water: Salt is said to have a
high solubility in water. However,
sand does not dissolve appreciably in water:
Sand has low or no solubility in water. If a substance does dissolve in water, three kinds of solutions
can be made:
1) Saturated - A solution is saturated if
it contains as much solute as it possibly can. At room temperature, 100 grams of water can dissolve a maximum
of 37 grams of salt. When these
conditions are achieved, the salt water solution is saturated.
2) Unsaturated - A solution that has less
than the maximum amount of solute that can be dissolved. At room temperature, any amount of salt
less than 37 grams in 100 grams of water would constitute an unsaturated solution.
3) Supersaturated - A solution that contains
more solute than it should, which results in a highly unstable solution.
If we were somehow able to get 40 grams of salt dissolved in water
at room temperature, the solution would be supersaturated.
How
to make a supersaturated solution:
Rock
Candy is made from a supersaturated solution of sugar water. Sugar is
dissolved in a big kettle of water until no more sugar dissolves at room temperature.
Then, the saturated solution is heated up. The higher temperature
allows for more sugar to be dissolved, so more sugar is put in. As more
and more sugar is put into the kettle, it dissolves, which makes the solution
saturated at the new higher temperature. Now, if the sugar is cooled
down very slowly, and no more sugar is added, the sugar will stay dissolved.
As the temperature cools, the sugar dissolved at that higher temperature
stays dissolved, and a supersaturated solution is made. At this lower
temperature, the solution is unstable, and by putting a small crystal of solid
sugar in the kettle, the extra sugar that is dissolved will attach itself
to the sugar, and grow crystals, or rock candy.
Effects on Solubility
Solubility can be affected by the temperature of the solvent.
The graph at right
shows the solubility of several solids at different temperatures.
Any
point below the curve indicates an unsaturated solution. At 25 OC,
an unsaturated solution of KNO3 would contain less than 40
grams of dissolved potassium nitrate. |
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| Diagram Courtesy of ChemCom 4th Edition |
Complete the following worksheet: Solubility and Concentrations
Links to more information/examples on Saturation and Solubility