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LOES SciSense Spring 2015
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2014 HoCoSTEMFestival Activity
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Episode 7 Crystal Candy
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PROCEDURES (followed by ScienceBuddies):
Day 1
To start this science fair project, cut two pieces of yarn. Each piece should be approximately 1 inch longer than the height of the glass jars.
Set one of the pieces of string aside and do nothing to it. Soak the other piece of string in a cup of water for 5 minutes.
After soaking, use your hand to squeeze the excess water from the string. Roll the string in 1 tablespoon of sugar on a plate. The string will be coated with sugar. These small bits of sugar are the seeds on which other sugar crystals might grow.
Lay both your seeded (sugar-coated) string and your non-seeded string on a piece of wax paper overnight. Make sure they are not touching.
Day 2
Prepare the strings.
Take your seeded string and tie one end to a screw, wooden bead, or other small object that can serve as a weight. It is ok if some of the sugar falls off while you're tying it to the weight. Repeat the process with the non-seeded string and a second weight. Be sure to use the same type of weight for each string.
Tie the other end of each piece of string to a skewer, Popsicle stick, or pencil.
Using a marker, color the edges of the skewer that is holding the seeded string. That way you will know later which string had sugar on it. Make sure to write down in your lab notebook the marking of your seeded string skewer in case you forget later.
Lower the weighted end of the seeded string into one of the jars and rest the skewer across the mouth of the jar. Roll the skewer to wind the string until the weight is suspended approximately 1 centimeter (cm) from the bottom of the jar, which you can measure with your ruler. Tape the string around the skewer so that the length of the string cannot change. Repeat this process for the non-seeded string, then take the skewers and strings out of the jars and set them aside.
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.
Caution
: get help from an adult when handling boiling water.
Boil enough water to fill both jars.
When the water is boiling, carefully pour it into the jars. You might want to use a funnel to avoid spilling too much water.
Let the full jars sit, with the hot water in them, until your sugar-water solution is ready.
Make the sugar-water solution.
Using a liquid measuring cup, add 1 cup of water to a pot. Bring the water to a rolling boil on the stove. Turn the heat down to low. Note: if you are using jars that are larger than 14 oz, heat 2 cups of water.
Using a dry measuring cup, add 2 cups of sugar to the hot water. Note: if you are using jars that are larger than 14 oz, add 4 cups of sugar.
Mix with a wooden mixing spoon until all the sugar has dissolved.
Turn the heat back up and wait until the sugar-water solution returns to a rolling boil. Make sure to keep stirring so the temperature is consistent throughout the solution.
Remove the boiling sugar-water solution from the stove.
Continue to add sugar 1 tablespoon at a time. Stir thoroughly after each added spoonful, making sure that the sugar is completely dissolved before adding another spoonful. Note: do not confuse the tiny little bubbles in the solution for undissolved sugar. You can tell them apart by stopping your stirring for a moment; the sugar will settle to the bottom of the pan, the bubbles will remain suspended throughout the solution.
Keep adding sugar until no more will dissolve in the solution. If you think you've added too much sugar to your solution, don't worry. Keep stirring and if even after a full 2 minutes of stirring, you have undissolved sugar at the bottom of your pot, return the pot to the stove. Heat the solution until it just begins to boil, then remove it from the stove. This should help you to get that last bit of sugar into the solution.
After the last bit of sugar has been dissolved, allow the solution to cool for 5 minutes.
Pour the hot water out of the preheated glass jars.
Caution
: the jars will be hot, so use oven mitts or pot holders to handle them.
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 containers.
Caution:
Be extremely careful when pouring the sugar-water solution; it is hot and will burn if spilled on your skin.
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.
Gently lower the weighted strings into the jars of sugar-water solution, one string per jar.
Securely tape the skewers holding the strings to the edges of the jars to prevent the strings from being accidentally jostled.
Loosely cover the jars with a paper towel to prevent dust and debris from flying in, while still allowing evaporation to occur.
Observations and Measurements
Look at your jars once a day. What do you see? Are there any crystals growing? Where are the crystals? Which string has more crystals: the one that was or wasn't seeded? Make a data table, like the one below, in your lab notebook and record your observations every day. While you actually prepared your strings on the "Day 1" step above, for the purposes of the experiment, Day 1 in your data table will be the day you made your solution and began running the experiment.
Make observations of your sugar-water solution jars for one week. On the seventh day, remove the strings from the jars and take measurements of your rock candy crystals.
If there is a layer of hardened sugar syrup coating the top of your jar, you can use a spoon to gently break that layer before pulling out your sugar crystals.
Briefly rinse the rock candy crystals in cold water, then leave them on a paper towel for 30 minutes to dry.
Using a ruler, measure the length of the rock candy, and the width at the widest point. Record your measurements in a data table, like the one below, in your lab notebook. Did seeding make a difference in the size of the rock candy that you grew?
Starting String ConditionsLength (cm)Height (cm)Seeded Not Seeded
Once you've recorded all your measurements and observations, you can enjoy all your hard labor by eating the rock candy you grew!
How many days did it take to get your first crystals? What was the difference in the coated and non-coated string?
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What do you think was an important factor in allowing your crystals to grow? Please explain.
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If you were to do this project again, what would you change and for what reason?
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