LSS_Solubility Lesson
Solubility
The relative concentrations of solutions are often described in terms of dilute and concentrated. It is important to note that these terms are not quantitative. A solution of 10 g of salt in 50 g of water is considered dilute when compared to a solution of 25 g of salt in 50 g of water. But, when compared to a solution of 1 g of salt in 50 g of water, the same solution would be concentrated.
It is not possible to dissolve unlimited amounts of solute in solvents. The amount of solvent that will dissolve is known as the solubility. Solubility is defined as the number of grams of a solute that dissolve in 100 g of water at a given temperature. The solubility varies with temperature, so it is imperative for the temperature to be stated. A solution that has the maximum amount of solute dissolved in the solution at that temperature is known to be saturated. A solution with less than the maximum amount of solute is known as unsaturated. If more than the maximum amount of solute is dissolved, the solution is said to be supersaturated. Note that supersaturated solutions are not easily made. Under normal conditions when more solute is added than can be dissolved in that amount of solvent, a supersaturated solution is NOT made. Instead, the maximum amount of solute that can dissolve will. And, the rest will remain undissolved on the bottom of the solution.
Go through the following slides from UCDavis to see representations of each of these types of solutions.
Factors Impacting Solubility
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The Scientific Method
Watch this video to review solubility and factors that affect it.
Temperature and Solubility
In a solution where the solute is a solid or liquid, changing the temperature changes the solubility of the solute. When the temperature of a saturated solution in dynamic equilibrium is increased, the equilibrium shifts so that the heat is used up. For most solids and liquid solutes, this equates to more solute dissolving in the solution. For a few solutes, when the temperature increases, the solute becomes less soluble. Ce2(SO4)3 is an example of this. Solubility curves show the changes in solubility of several solutes in 100 g of water as the temperature is increased.
Look at NaCl at room temperature, approximately 25oC, as an example. If we take 30.0 g NaCl and add it to 100 mL of water, we will have an unsaturated solution.
If we take 40.0 g NaCl and add it to 100 mL of water, we will have a saturated solution with 4.0 g of NaCl undissolved at the bottom of the solution.
Note - We will discuss the solubility of gases in the next module.
Remember to work on the module practice problems as you complete each section of content.
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