Part 1:

 

Measure 1.0 mL of water into a test tube. Add 25.0 g of sodium thiosulfate (hypo).

1. Hypothesize: Do you think the crystals will dissolve?
2. What type of solution have you prepared?

To dissolve the crystals, carefully heat the unstoppered test tube in a flame. Point the mouth of the test tube AWAY from people, toward the wall, until the crystals go into solution.

3. While hot, what type of solution is this, unsaturated, saturated, or supersaturated? How could you test this?

After heating, the mixture should become homogeneous. Carefully remove the test tube from the hot water bath and place the test tube into a cool water bath. Let the solution stand undisturbed for about 5 minutes, or until the solution cools to room temperature. Record your observations.

4. Hypothesize: When cooled, what type of solution is this?

To test your prediction, use a pair of forceps to add one crystal of hypo to the cool solution. Record your observations. Feel the test tube. It started at room temperature.

5. Is the process of recrystallization endo or exothermic?

 

Part 2:

 

Measure 1.0 mL of water into a test tube. Add 1.0 g of sodium thiosulfate (hypo) crystals.

6. Hypothesize: Will the solution be unsaturated, saturated, or supersaturated?

Stopper and shake. Feel the bottom of the test tube.

7. Is this process of dissolving exothermic or endothermic? Did the crystals dissolve? ecord your observations.

 

Part 3:

 

Measure 1.0 mL of water into another test tube. Add one crystal of hypo.

8. Hypothesize: Will the solution be unsaturated, saturated, or supersaturated?
   

Stopper and shake for 5 minutes.

9. Did the crystal dissolve? Record your observations.