Name:_______________________

Unsaturated, Saturated, and Supersaturated Solutions and Temperature Change.

A saturated solution contains more solute in a given volume of solvent than an unsaturated solution.  A supersaturated solution contains more solute in a given volume than would normally be present at a particular temperature.  A supersaturated solution is unstable.  When a crystal of solute is added to a supersaturated solution, excess solute crystallizes out of solution: the remaining solution is saturated as it normally would be at that temperature.  When a crystal of solute is added to an unsaturated solution, the crystal will dissolve.  Most of the time, when the temperature of a solvent increases, the solubility of the solute increases in a given amount of solvent. 

Objectives:

  1. Students will compare and contrast the physical properties of unsaturated, saturated, and supersaturated solutions.
  2. Students will discover the effects of temperature change on solute solubility and color intensity.

Materials:

 Sodium acetate

three large test tubes

test tube holder

Bunsen burner

Thermometer

Stirring rod

Test tube rack

Graduated cylinder

Balance

Procedure:

  1. Prepare a saturated solution of sodium acetate:  In a large test tube, dissolve 6.5g of sodium acetate in 10.0 ml of distilled water at 25° C.  If you cannot get all of the solute to dissolve in you solution after patiently stirring, let the mixture settle and pour off most of the liquid into a new clean test tube without getting any of the solid into the new test tube.
  2. Prepare an unsaturated solution of sodium acetate:  In a large test tube, dissolve 3.0 g of sodium acetate in 10.0 ml of distilled water at 25 °C.
  3. Prepare a supersaturated solution of sodium acetate:  In a large test tube, add 12.0 g of sodium acetate to 10.0 ml of distilled water and gradually heat the test tube contents in a water bath on a hot plate until all the sodium acetate is dissolved.  Carefully place the test tube into an ice bath and let it cool undisturbed. 
  4. When all of the solutions have cooled to about room temperature, add a small crystal of sodium acetate to each test tube, observe and record what happens.
  5. Observe the appearance of all three solutions, recording observations.

Questions and Conclusion: 

  1. What was the appearance of each sodium acetate solution before a crystal of each compound was added?

  1. How did the solutions change when the crystals were added?  In some cases, did the solution become heterogeneous mixtures?  Is so, which ones?

  1. How does the increase in temperature affect the solubility of a solute in a solvent?