Sugar Crystal Science Lesson

Teaching the Three States of Matter with Rock Candy

© Susan Hyde

Sep 12, 2007

Crystal growing experiments teach students more about molecular structure and the science behind the three states of matter. This easy and edible kitchen experiment uses kinesthetic learning strategies to illustrate how molecules interact to create gases, solids, and liquids.

Content Areas: Scientific Method, Chemistry

Materials:

• Cool water
• Ice cubes
• Boiling Water and 1 cup ladle
• Six sheets of paper labeled with the letter "O" and three labeled with the letter "H"
• Tape
• Several bags of sugar (sucrose)
• Glass jars
• Plastic spoons
• Rough dowels or rounded bamboo chopsticks
• Food coloring
• Magnifying glass
• Teacher created worksheet for recording materials, procedures, hypotheses, daily observations and results.

Vocabulary List:

• Atom
• Molecule
• Crystal
• Gas
• Liquid
• Solid
• Dissolve
• Solution

Group Activities:

• Show the students a cup of cool water, the ice cubes, and steaming water. Ask the students what the water, ice, and steam have in common (they are all forms of water). Explain to students that these familiar water forms exemplify the three states of matter: liquid, solid, and gas.
• Ask for three sets of three student volunteers. In each group, label one student the "H" paper. On the other two, tape the "O" labels. Ask the two "O" students to hold hands with the "H." Explain to the class that the "H" stands for hydrogen gas and the "O" represents oxygen gas. Explain that, when these molecules combine in this way, a water molecule is formed. Students might be interested to know that there are almost 850 quintillion (that's 18 zeros) individual H2O molecules in one drop of water.
• Ask the groups student volunteers to slowly sway. Explain that solids(in this case, ice) are a result of slow moving molecules that can vibrate but not flow past each other. Solids occur at lower temperatures. You might add that molecules can't stay entirely still any more than students can!
• Ask the student "molecules" (still holding hands) to walk slowly around each . Explain that liquidsare the result of molecules gliding past one another. Ice melts to water when the temperature is increased.
• Finally, ask the "molecules" to jog around each other. The students will likely find it difficult not to run into one another. Explain that, when water is heated to boiling, the molecules become very energetic and bump into one another. The resulting steam is an example of the third state of matter: gas.

Crystal Growing Activity:

1. Assist students by carefully pouring one cup of water into each clear plastic cup.
2. Students will use the plastic spoons to pour sugar into the hot water. Ask them to note the sugar quicklydissolvesin the hot water. Explain that each sugar molecule remains intact when this occurs, but that the particles are so small that they can't be seen. Students should continue to add sugar until it no longer dissolves in the water (sugar will begin to rest at the bottom of the cup.
3. Stir a two or three drops of food coloring into sugar solution with the dowel and then leave the dowel in the water
4. Place a paper towel over the jar (stick the dowel through the paper to hold it in place)
5. Record changes to the dowel each day (use magnifying glasses).
6. In one week, students will have a stick of rock candy created as the water cools and the molecules separate arrange into orderly patterns called sugar crystals. Contrast the crystals with the "invisible" sugar in the original solution.

Enjoy the rock candy!

Crystals teach properties of matter.

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