Alum Crystals

Following is a science process with the purpose of growing a large crystal of alum. A recipe (procedure) is given.

Following this crystal growing process, clues for a crystal growing science project is given.

Purpose: To grow a large alum crystal.

Procedure:

Step 1: Label two clean pint glass jar A and B.

Step 2: Pour 1 cup of hot tap water into a jar A.

Variables: amount of water, temperature of water, size of growing jar, type of jar (plastic)

Step 3: Add 1 teaspoon of alum to the hot water. Stir until all the alum dissolves. Repeat this step until the alum stops dissolving. (Have available 6 tablespoons (18 teaspoons) of alum.

Variables: amount of alum added

Step 4: Loosely cover the jar with a paper towel (to keep dust out).

Variables: the tightness of the covering

Step 5: Allow jar A to sit at room temperature in a place where it will not be disturbed overnight.

Variables: temperature of environment for the jar, how long it sits, how stationary the jar is kept

Step 6. Pour the alum solution from jar A into jar B. Use a metal spoon to scrap crystals that formed in the bottom of jar A. These are called seed crystals. (Wash and dry jar A–you may need it later.)

Step 7: Use nylon fishing line to tie around the largest and best-shaped seed crystal.

Variables: type of line, size of seed crystal

Step 8. Tie the free end of the fishing line to a pencil, and then suspend the seed crystal into the solution in jar B. Roll the pencil so that fishing line is long enough for the seed crystal to be in the center of the alum solution while the pencil rests across the mouth of the jar.

Variables: position of the seed crystal in the alum solution

Step 9: Set jar B with the alum solution and seed crystal in a place where it will be undisturbed at room temperature, and visible for observing the seed crystal.

Variables: Temperature at which the crystal is grown

Step 10: Loosely cover jar B with a paper towel. Make observations for 7 or more days.

Variables: jar covering

Trouble Shooting

1. If you see crystals growing around the sides and bottom of the jar, carefully remove the line with the attached seed crystal. Pour the alum solution into a clean jar, and then hang the seed crystal as before.Note: make sure that no crystal fall into the clean jar.

2. When the alum crystal stops growing, raise it and hang it in an empty jar until you can repeat steps 1 through step 6 to prepare more alum solution. When the alum solution is at room temperature, lower the crystal into the jar as in step 8.

Crystal Growing Science Fair Project

For a science fair project, select one of the variables and repeat the crystal growing process making changes in that one variable.

For example, in step 9, use the variable of temperature. Your project question would be:

How does the the temperature affect how large an alum crystal grows?

Janice VanCleave’s Guide to More of the Best Science Fair Projects