Unsaturated, Saturated and Supersaturated Solutions -

Their Effects on Solution Color Intensity

The two parts of a solution are the solute and the solvent. The solvent is the substance doing the dissolving and the solute is the substance being dissolved. When a solute is first placed in a solvent, many particles leave the surface of the solute and go into solution. As the number of solute particles in solution increases, some of the dissolved particles crystallize on the surface of the undissolved solute. When the rate at which undissolved solute goes into solution equals the rate at which dissolved solute comes out of solution, a condition exits called solution equilibrium. Solution equilibrium is a dynamic process, meaning that there is a continuous interchange between the dissolved and undissolved portions of the solute. As a result of this interchange, there is no net change in the number of dissolved or undissolved solute particles.

A solution in which an undissolved solute is in equilibrium with the dissolved solute is called a saturated solution. A saturated solution is one that has dissolved in it all the solute it can normally hold at a given temperature. A saturated solution at one temperature will contain a different amount of dissolved solute than will a saturated solution of the same solute at another temperature. A solution that contains less solute than it can hold at a given temperature or less than the saturated amount is an unsaturated solution. A solution that contains more solute than the saturated amount at a given temperature is a supersaturated solution.

In Part 1 of this investigation, you will prepare a saturated, unsaturated and supersaturated solution. You will then add a small amount of the solute to each solution and observe what happens. In Part 2 of this investigation, you will evaluate paint color intensity based on what you learned about saturated, unsaturated and supersaturated solutions.

Pre-lab Questions.

1. Is a solution a homogeneous or heterogeneous mixture?

2. Draw a picture illustrating solution equilibrium.

3. Define solubility.

4. Describe the effect of an increase in temperature on the solubility of most solids dissolved in water.

5. You chemistry teacher has asked you to prepare a saturated solution of glucose, C₆H₁₂O₆. The solution is to be made at room temperature and you have no measuring devices. What observations can you make about the solution to be assured that the solution is saturated?

6. Predict what will happen when you add a small amount of solute to each of the following:

a. a saturated solution

b. a unsaturated solution

c, a supersaturated solution

Procedure

Part 1.

1. Label three test tube as follows:

"S" for saturated; "US" for unsaturated; and "SS" for supersaturated.

2. To the test tube labeled saturated, add 4.65g of sodium acetate, NaC₂H₃O₂, and 10.0 mL of distilled water.

3. To the test tube labeled unsaturated, add 3.00g of sodium acetate, NaC₂H₃O₂, and 10.0 mL of distilled water.

4. Agitate each test tube for 5 minutes.

5. To the test tube labeled supersaturated, add 7.00g of sodium acetate, NaC₂H₃O₂, and 10.0 mL of distilled water. Place the test tube in a boiling water bath until all of the solute is dissolved.

6. Place each test tube in a test tube rack label with your name. Cover each test tube with a small piece of parafilm. Allow the solutions to cool overnight without being disturbed.

Next Day

7. Observe the appearance of all three solutions, recording observations in Data Table 1.

8. To the saturated solution, add a small amount of NaC₂H₃O₂. Agitate the test tube for several minutes. Observe and record what happens to the added solute in Data Table 1.

9. To the unsaturated solution, add a small amount of NaC₂H₃O₂. Agitate the test tube for several minutes. Observe and record what happens to the added solute in Data Table 1.

10. To the supersaturated solution, add a small amount of NaC₂H₃O₂. Observe and record what

happens to the solution when the additional solute is added in Data Table 1

Data Table 1.

	Observations before additional solute is added	Observations after additional solute is added
Saturated
Unsaturated
Supersaturated