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Growing rock candy crystals
Transcript of Growing rock candy crystals
Annie Skinner and Alyssa Young
We predict that the string with excess sugar will have a faster growth rate and larger rock crystals than the one without.
•Yarn or cotton string (about 1.5 feet)
• Tablespoon measuring spoon
• Small plate
• Granulated white sugar (3 cups)
• Wax paper
• Screws, wooden beads, or other small nontoxic objects to use as weights (2)
• Wooden skewers, Popsicle sticks, or pencils (2)
• Marker to write with
• Ruler (with centimeter markings)
• Glass jars, make sure they are identical in size and shape (2)
• Measuring cup (for liquid ingredients)
• Measuring cup (for dry ingredients)
• Wooden mixing spoon
• Pot holders
• Paper towel
• Lab notebook
1. Prepare the strings.
2 .Preheat the glass jars. This will ensure that you are not adding your hot sugar-water solution to a cold jar, which would result in a dramatic temperature change that might make small crystals form along the glass. The small crystals would disrupt your rock candy formations.
3. Make the sugar-water solution. Start by adding 2 cups of water to a pot.
Then, add 2 cups of sugar to the hot water. Mix with a wooden spoon until all the sugar has dissolved. Then, turn the heat back up and wait until the solution returns to a rolling boil. Continue stirring. Then, remove the boiling sugar-water solution from the stove. Keep adding sugar 1 tablespoon at a time, making sure that the sugar is completely dissolved before adding another spoonful. Continue adding sugar until no more will dissolve.
4. After the last bit of sugar has been dissolved, allow the solution to cool for 5 minutes.
Rock candy is a collection of large sugar crystals that are "grown" from a sugar-water solution. Sugar can come in many different physical states. Crystals form when the smallest particles of a substance (molecules) arrange themselves in an orderly and repetitive pattern. There has to be enough molecules in one area that they have a high chance of bumping into one another. This happens when a solution is saturated. In the rock candy, the liquid is water and the compound is sugar.
In a saturated solution, the molecules bump into one another frequently because there are so many of them. Occasionally when they bump into each other, the molecules end up sticking together. This is the beginning of the crystallization process. Once several molecules are already stuck together, they actively attract other molecules to join them. This slow process is how the crystal "grows".
Will a string seeded with sugar grow faster, more and larger rock candy than one without?
5. Pour the hot water out of the preheated glass jars.
6 After the sugar-water solution has cooled for 5 minutes, pour the solution into the two preheated glass jars, dividing the liquid equally between the two
7. Using pot holders, move the jars of sugar-water solution to a place where they can be left undisturbed for one week. Place both jars in the same location. Large fluctuations in temperature can interfere with the crystallization process, so avoid putting the jars in places that get direct sunlight, or are near a heating or cooling vent.
8. Gently lower the weighted strings into the jars of sugar-water solution, one string per jar.
9. Securely tape the skewers holding the strings to the edges of the jars to prevent the strings from being accidentally jostled
Nothing happened on the first day because it was only just set up and needed to sit before anything would happen.
Independent Variable: One string is seeded with sugar, one string is not.
Dependent Variable: The speed, amount and size of sugar crystals that grow.
Controlled Variables: Size of jars, type of sugar, amount of sugar-water solution in each jar, type of yarn, length of yarn, place of each jar, type of weight, etc.
No signs of growth on string, but small pieces of sugar collected on side of jar.
Doesn't look like much is happening, but the top of the liquid is starting to turn hard.
Small amounts of sugar starting to form on both strings and top of them are completely covered in a hard sugar.
Sugar crystals forming faster on seeded string, small crystals still on unseeded string.
Many, medium-large crystals formed on seeded string whereas only a few crystals on unseeded string but about the same size.
Final day of experiment and the seeded string is filled with crystals where the unseeded is about the same a day 6 and the bottom of both jars are covered in a hard sugar substance.
Our hypothesis was correct in that the seeded string grew much faster and more sugar crystals over the unseeded string, but the overall size of the crystals in both were about the same.
Science Buddies - http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p005.shtml#summary
R. Semper. Science of Sugar - http://www.exploratorium.edu/cooking/candy/sugar.html
P. Boyle and T. Linden. Frequently Asked Questions About Crystals For Students - http://www.xray.ncsu.edu/student_faq_xtal.html