Hands-on science (No lab required).

After reading "Rockin' Gems" (p. 8), find out how crystals grow and what makes these sparklers look different from each other.

MATERIALS

safety goggles * * 2 spoons (teaspoon size) * alum (10 ml, or 4 tsp) * 6 disposable plastic bowls * masking tape * marker * measuring cup * warm tap water (400 ml, or 1.5 cups) * table salt (10 ml, or 4 tsp) * Epsom salt (10 ml, or 4 tsp) * sandpaper (10 cm by 10 cm, or 4 in. by 4 in.) * magnifying lens * pencil and paper 

* Wear safety goggles throughout this activity.

PROCEDURE

1 Measure 10 ml (4 tsp) of alum and place into a plastic bowl. The alum will be one of your solutes, or the dissolved substance in a solution.

2 Use a piece of masking tape and a marker to label the bowl with its contents.

3 Add 60 ml (1/4 cup) of warm water to the bowl that contains your solute.

4 Stir the mixture with a teaspoon until all the solute is dissolved in the water.

5 Repeat Steps 1 to 4 with a fresh bowl. This time, use table salt in place of alum.

6 Repeat Steps 1 to 4 with a fresh bowl. This time, use Epsom salt in place of alum.

7 Rub a piece of sandpaper across the bottom of each of three empty plastic bowls until the bottom of each bowl is rough with scratches.

8 Repeat Steps 1 to 6. But this time, use the sandpaper-scratched bowls. Be sure to label these bowls as scratched.

9 Place all 6 bowls by a sunny window. Leave them for 5 days.

10 Each day, observe the contents of the bowls with a magnifying lens, and record your observations. For example, do you see any crystals in the water? When you do see crystals forming, make a rough sketch of each.

CONCLUSIONS

1 What happened to the alum solution? Table salt? Epsom salt?

2 In which bowl--smooth or scratched--did you observe crystals growing the fastest? Why might this be?

3 Compare the crystal shapes formed by each solute. How are the crystals different from each other? How are they similar?

ANSWERS

1. By the fifth day, you should have observed the following: small hexagonal crystals in the alum solutions; square-shaped crystals in the table-salt solutions; long, spiky crystals in the Epsom solutions.

2. Crystals began forming sooner in the scratched bowls, That's because the scratches create more surface area, which can serve as sites that just-forming crystals can attach to. The process of crystal growth occurs in stages. First, the solute, or the substance that is dissolved in the water, separates from the water solution. Then, the solute molecules join together in an orderly pattern to form a crystal When many crystals clump together, larger crystals form With more sites for crystals to attach to, such as the scratches, large crystals form sooner.

3. The salt crystals should have a cubic shape. The Epsom-salt crystals should be long and thin, and overlap, like a pile of tiny sticks. This shape is described as monoclinic, meaning the crystals are like crooked cubes. The alum crystals should form hexagonal-shaped chunks, They are all similar because they have patterns that repeat, which is the definition of a crystal.