Objective:

To observe the relationship between cooling rate and crystal size.

Materials :

Alum or Copper Sulfate (Alum is a pickling spice and can be purchased in the grocery store)
Boiling water
Thread and 2 - 3 pencils
Pyrex or kymax container
Refrigerator, Freezer or cooler with ice
Magnifying glass
Paper and pen or pencil to record your data

Procedure:

1. Add Alum (or copper sulfate) into the boiling water into two separate Pyrex containers until no more will dissolve.(make a hot concentrated or supersaturated solution)
2. Place a piece of string attached to a pencil into each of the warm solutions and record date and the time and the room's temperature..
3. Allow one of the solutions to cool at room temperature.
4. Watch for crystals to form along the sides of the container and on the thread. Record the date and the time. ( You will have to wait for the solution to evaporate which is a cooling process for large crystals to form-Humidity and any movement of the solution may effect your results) Set the time for observing at convenient intervals during the first day and then once or twice during the following days.
5. Draw and describe the size of the crystals. ( You may save the string of crystals and tape them on appropriately colored construction paper so students may compare the string of crystals side by side- label each string for comparison)
6. Place a new string in the remaining solution.
7. Record the date and time and any observations.
8. Cool the second solution in a refrigerator or in a cooler with ice.
9. Record the time, date and temperature of the cool place
10. Check the cooling solution every 20 minutes
11. Time how long it takes for crystals to form.
12. Draw and describe the crystal size.
13. Compare with the size of the crystals cooled at room temperature.
14. Prepare a new solution or heat the solution again and place in a piece of string into this third solution. Record the date and time and temperature of the freezer.
15. Place the warm solution in a freeze.
16. Check the solution every10 to 20 minutes.
17. Record the date and time when crystals form.
18. Compare the size of the crystal size with the refrigerator and room temperature crystals