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| Alum crystal, courtesy of Wikipedia Commons. |
This year my son's classroom is growing alum crystals for their group science fair project. Already it has yielded exciting results! If you need a project that is fairly easy for elementary students to conduct, this is a good one.
Even after the first day of creating the seed crystals, we have great variation in seed-crystal sizes among students. The students record the pH of their solution every day in their science journals, and we also have a measure of what I like to call the "cloudiness factor" of their solution, which is basically a simple way of describing how cloudy each student's water was when they were dissolving their alum in solution. Over the next couple weeks, the students will begin to hypothesize about the relationship between crystal growth and the basic chemical and physical properties of their initial crystal-growing solution.
If you want to try growing alum crystals at home, here is what you'll need.
Materials
2 jelly jars (big enough to hold at least 1 cup of water, each, and to withstand high temperatures)
1 - 2 cups RO (reverse osmosis) or distilled water
stainless steel stirring spoon
dental floss
pencil
Methods
Heat water to near boiling.
Pour 1 cup of water into one of the jelly jars.
Slowly pour some of the alum (approx. 1 - 1/2 tablespoons) into the water.
Stir until all the alum dissolves in the water.
Add more alum slowly, continuing to stir, until it no longer dissolves in the water (it will be approximately 2 and 1/2 tablespoons, more or less, when you're done).
Set aside in quiet place where it won't be disturbed, and cover with paper towel overnight.
Day 2:
You should have several seed crystals growing along the bottom of your jar.
Use a spoon to pick your favorite one. Set aside.
Decant the solution into the 2nd jar, leaving the remaining crystals behind. You can discard these or set them aside for another project.
Tie a long string of dental floss around the crystal. It should be long enough to wrap plenty of extra string around the pencil on the other end of the string.
Hang the pencil over the top of the 2nd jar, with the string and crystal hanging down into the solution.
Roll up the pencil and string until the crystal is hanging just beneath the water line.
Clean the 1st jar and leave to dry for the next day.
Day 3 and beyond:
Repeat the process of pouring the solution into the other jar and rehanging the crystal until it stops growing! Sometimes this can take up to 2 weeks, depending on how concentrated your solution was to begin with.
You will be amazed at the results!
