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.
- Students will compare and contrast the physical properties of unsaturated, saturated, and supersaturated solutions.
- Students will discover the effects of temperature change on solute solubility and color intensity.
three large test tubes
test tube holder
Test tube rack
- 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.
- 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.
- 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.
- 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.
- Observe the appearance of all three solutions, recording observations.
Questions and Conclusion:
- What was the appearance of each sodium acetate solution before a crystal of each compound was added?
- How did the solutions change when the crystals were added? In some cases, did the solution become heterogeneous mixtures? Is so, which ones?
- How does the increase in temperature affect the solubility of a solute in a solvent?