Sugar Crystallization

Research Questions

• What does applying heat to the water before adding the sugar allow it to do?
• How do natural crystals form?
• What happens when a solution is supersaturated?
• How is each type of sugar derived and what are its chemical properties?

Have you ever wondered how candy is made? Rock candy is one of the earliest forms of sweets and can be easily created in your own home with basic ingredients and some patience.

When people think of sugar, the first thing that comes to mind is usually white granulated sugar, which is the most common. However, there are actually different types of sugars that are different colors, textures, forms, consistencies, and/or obtained in different ways and from different sources. For example, brown sugar is tinted brown because there is molasses in its composition. Powdered sugar is actually super-crushed regular white granulated sugar that is usually used in baking.

Rock candy is created through processes called crystallization and supersaturation. There is an excess amount of sugar in the sugar vs. water ratio, thus crystals form as the water gradually evaporates (turns from a liquid to a gas). The cool thing about rock candy is that the shape of the candy is actually the shape of the tiny individual sugar crystals magnified and is basically just many tiny sugar crystals grown together.

In this experiment, you are dealing with heat and an open flame. Keep any other materials away from the flame. The liquid inside will be boiling hot. Adult supervision throughout the experiment is also highly recommended.

Materials:

• 2 cups of regular granulated cane sugar (white)
• 2 cups of brown sugar
• 2 cups of powdered sugar
• 6 cups of water (two cups for each type of sugar)
• 3 small and thoroughly cleaned transparent glass jars (preferably the same size)
• Cotton string (found in hardware stores, or craft stores)
• 3 screws, galvanized washers, paper clips, or just some kind of small weight to hang on the string
• 3 pencils to suspend the string in the jar (length must be wider than the opening of the jar)
• 3 labels, a notepad/notebook for notes, and a pen/marker
• Camera
• Small saucepan 
• Wooden spoon
• Measuring cup
• Wax paper
• Pair of anti-heat gloves, pot holders, or oven mitts

Experimental Procedure

1. Gather the materials in one spot: this is a nice habit to learn so that you don't have to fumble around for materials during the experiment and so that you can enjoy the whole experience!
2. Label your three glass jars “White Sugar”, “Brown Sugar”, and “Powdered Sugar.” Set them aside.
3. Making sure an adult is there to supervise, turn the stove up to medium-high heat and boil the water in the saucepan.
4. Take two cups of white sugar and carefully pour them into the boiling water, stirring continuously with a wooden spoon to help the sugar complete dissolve. When the solution reaches a rolling boil, it's ready. Note how fast it dissolves. Remove from heat.
5. Take the glass jar labeled “White Sugar” and carefully pour the solution into the jar. Take a small piece of wax paper and cover the opening of the jar.
6. Measure a piece of cotton string that is two-thirds the depth of your glass jar. Tie the small weight you chose to one end of the string and tie the other end to the pencil. Carefully dip the string (washer end first) into the solution and let it soak for a couple minutes. Then remove the string, straighten it out, and lay it flat to dry on wax paper for three days (leaving the pencil and the washer attached).
7. Repeat steps 3–7 for the Brown Sugar and the Powdered Sugar. Important: remember which string went in which solution! Also, be sure not to throw out the sugar solution in the jars. You'll be using it after the three days have passed.
8. After the three day waiting period for prepping the strings is over, simply suspend the three cotton strings in their respective jars (with the liquid sugar solution in the jars) at room temperature for about one week. Do not touch the strings as movement will disturb the growth process. You should observe, note, and, if possible, take photos of the day-to-day growth of crystals for each jar. A chart is included below as a suggestion.
9. After one week, you should see at least some sugar crystals. They should be clear and in rather spiky and sharp formations. Compare and contrast the growth, size, and shape of the sugar crystals in all three jars. Are there any differences? Similarities?

Terms/Concepts: Crystallization, Crystal Nucleation, Supersaturation, Solutions and Mixtures, Sugar and Sucrose, Heat, Dissolve, States of Matter, Evaporation

References:

• http://en.wikipedia.org/wiki/ROCK_CANDY
• http://www.stevespanglerscience.com/experiment/00000078
• http://www.cheresources.com/cryst.shtml
• Geankoplis, C.J. (2003) "Transport Processes and Separation Process Principles". 4th Ed. Prentice-Hall Inc.
• R. F. Symes, R. R. Harding (2007) “Eyewitness: Crystal & Gem”. DK Publishing.