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Crystals (page 2)

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Author: Janice VanCleave

Design Your Own Experiment

  1.  
    1. Will sugar crystals form from a solution containing a mixture of different-shaped sugar molecules? Heating a sucrose solution to a high temperature results in the breakdown of some of the sucrose molecules into the smaller sugar molecules of glucose and fructose. An acid, such as cream of tartar, speeds up this breakdown.
    2. Determine whether sugar crystals will grow in a mixture of glucose, fructose, and sucrose by adding together 1-1/4 cups (313 ml) of sugar, 1 teaspoon (5 ml) of cream of tartar, and 1/2 cup (125 ml) of distilled water. Place the mixture in a small saucepan and heat to boiling while stirring continuously. Boil for five minutes. Cool to room temperature before pouring into a clean soda bottle. Hang a cotton string in the bottle, as was done in a previous experiment. Place the bottle where it can remain undisturbed for two or more weeks. Make daily observations of the contents of the bottle.

    3. Another method of testing the crystal growth in a solution of different-shaped sugar molecules is to repeat this experiment replacing the sugar and cream of tartar with 1 cup (250 ml) of sugar and 1/4 cup (63 ml) of white corn syrup.
    4. Honey often his white corn syrup added to it to prevent sugaring (sugar crystal formation). If pure honey is available, test the effect of sugaring of the honey with and without the addition of white corn syrup. How much corn syrup is needed to prevent sugaring? Increase the speed of the sugaring of the honey by placing it in a refrigerator.
  2. Are all crystal shapes the same? Grow crystals form supersaturated solutions containing solutes such as table salt, rock salt, alum, and/or Epsom salt.
  3. How do the crystalline stalagmites (formations growing up from the floor) and stalactites (deposits hanging from the ceiling) form in caves? Simulate the formation of these structures by filling two baby food jars with Epsom salt. Add water to cover the Epsom salt in each jar and stir. Cut a cotton string 12 inches (30 cm) long and tie a washer on each end. Set the jars on a cookie sheet and place one washer in each jar. Position the jars so that the string hangs between them with the lowest part about 1 inch (2.5 cm) above the cookie sheet (see Figure 25.3). Allow the jars to stand undisturbed and out of any draft for one week. You can use pictures of the development of the formations as part of a project display. Information about the chemical reactions involved in these formations can be found in an experiment called "Fake" (p. 30) in Janice Van-Cleave's Earth Science for Every Kid (New York: Wiley, 1991) and in other earth science texts.
  4. Nature's Jewels

Get the Facts

  1. The smallest portion of a crystal is called a unit cell. Use a chemistry text to find the shapes of the seven basic unit cell structures. Inexpensive samples of crystals representing the different cell structures can be purchased at rock and mineral shops and displayed along with diagrams of the crystalline systems.
  2. What binding forces keep crystals together? Every crystal can be classified by one of four types of lattice structures: ionic, covalent network, metallic, or covalent molecular. Use a chemistry text to find description of the binding forces for each classification. Describe the forces in each and, by means of a chart, represent crystal examples of each type of lattice structure.
  3. What type of crystals are found in rocks? Do all rocks contain crystals? Crystals are formed when magma (hot, liquid rock) cools. How does the cooling rate of magma affect the type of crystal formed? Use an earth science text to find the answers to these questions and to discover more about crystals formed in nature.
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