Growing Crystals

FIELD: Earth Science DURATION: 1.5 hr w/daily observations
OBJECTIVE: Students will know how crystals form.
METHOD: Students grow simple crystals in glass jars using household ingredients.
KEY VOCABULARY: Crystal. GROUP SIZE: Any

BACKGROUND:

Crystals are solids that form by a regular repeated pattern of molecules connecting together. In some solids, the arrangements of the building blocks (atoms and molecules) can be random or very different throughout the material. In crystals, however, a collections of atoms called the Unit Cell is repeated in exactly the same arrangement over and over throughout the entire material.

Because of this repetitive nature, crystals can take on strange and interesting looking forms naturally. When we grow crystals we are separating all the building block molecules into individual units in water and letting them fall naturally into their appropriate place in the repetitive structure as the water evaporates.

In this experiment you dissolve crystallizing molecules in fluid and create crystal formations as the fluid evaporates.

MATERIALS (per group):

CRYSTALS ON STRING
Baking soda - 3 tsp.
Water - 1/2 cup
Electric hot plate
String - 10 cm (5-6 in)
Small weight for string (e.g. fishing weight)
Clear glass or vial.
CRYSTAL GARDEN
Ammonia - 2 tbsp.
Water - 2 tbsp.
Iodine - 10 drops
Glass pan
Food coloring - 10 drops
Small lumps of coal or corks
Salt - 2 tbsp.
Mercurochrome (bluing) - 10 drops

PROCEDURE:

CRYSTALS ON STRING
1. Put 1/2 cup water in pan.
2. Dissolve in as much baking soda as possible, stirring in 1 teaspoon at a time.
3. Heat the solution (do not boil).
4. Remove from heat, stir, and add more baking soda until no more will dissolve.
5. Cool solution.
6. Pour into a clear glass.
7. Tie the weight onto the end of the string and hang into solution.
8. After several days crystals will begin growing on the string as the water evaporates.
 
CRYSTAL GARDEN
1. Arrange the coal or corks along the bottom of the glass dish.
2. In another container mix 2 tablespoons of salt, ammonia, water, and mercurochrome.
3. Pour this solution over the coal or corks.
4. Scatter ten drops of mercurochrome, iodine, and food coloring over the top.
5. A crystal garden will begin to form in several days as the moisture evaporates.
6. Add more of the solution to increase the size of the crytals.

EXTENSIONS:

1. Observe the growth of crytals over time and sketch their appearance each day. Compare and contrast the two types of crystals. Do they look the same? What other crystals are there in the world?


Created April 24, 1997 by Danica Nuccitelli.
Maintained by danica@mills.edu.
Last updated April 24, 1997.