ISCI 172 Chemistry and Physics Lesson Plan Sheet
Type of Lesson
Chemistry
Activity Name:
Rock Candy
Learning Style:
Visual
Kinesthetic
Topic:
Food Chemistry
Grades Level Lesson is Appropriate For:
All!
Materials Needed:
Cane sugar (You’ll have great results with Imperial Sugar or Dixie Crystals.)
Water
Large glass container (microwave-safe)
Smaller glass jar
Measuring cups
Heavy stirring spoon
Pencil
Food coloring
String (new preferred)
Scissors
Wax paper (or parchment)
Time considerations:
A couple of days for the crystals to form
Brief description of Activity/Procedures (please be as specific as possible so others
can use it. Add any web addresses that you can to help others)
1. Pour about 3 cups of granulated cane sugar into the large glass container.
2. Add 1 cup (237 ml) of water to the sugar. Watch what happens as the water
bubbles through all that sugar. There’s a lot going on in the container already.
Use the heavy spoon to thoroughly stir the water (a solvent) and the sugar (a
solute) together to make a solution. It will be very viscous (thick) and heavy
because there’s a lot more sugar than water in there. Stir it well!
3. An adult must help with this Step! You need to give the water some help with
all that sugar so warm up the water. If the container is microwave-safe, put
the solution in the oven and heat it for two minutes on high. (You can use a
cooktop to heat the solution if you prefer.) Heat the solution to the boiling
point.
4. Move the stirred solution to the microwave (or cooktop) again and heat it on
high for another two minutes. Don’t let the solution boil over.
5. Add 3-7 drops of any food coloring to the mixture and stir it in thoroughly.
6. Pour the colored solution into the smaller glass container.
7. You need to use clean string and that’s why new is preferred. On an old roll,
unroll some until you get a layer or two under the top layer. Tie the string to
the middle of the pencil. Use the scissors to cut off a length longer than the
small container is tall. Lay the pencil on top of the small container and trim
the string so it’s about 2/3 the height of the container. You want it shorter
than the container.
8. Holding the pencil, lower the string into the solution and let it soak for a
short time. You want the solution to soak through the string. Lay the pencil
and soaked string on a piece of wax paper so the string is perpendicular to
the pencil. Allow the solution to cool to room temperature and the straight
string to dry completely.
9. As it cools, the solution becomes more viscous so it might be a trick to push
the dried string into it again. You may have to use a slow steady pressure to
get it to sink deeply into the solution. You’ll need to allow the string to soak
in the solution for a week, too. A paper towel over the container will keep
dust and goobers away from your candy – uh, your science experiment. Keep
track of changes in the solution and the growing crystals in the solution but
don’t disturb them by moving them. Pictures are a good idea!
10. When you’re ready for the big reveal, lift the pencil and pull the string loaded
with crystals out of the jar. Lay them on some wax paper and look closely at
what grew on the string. Of course, a taste test will have to be a part of your
analysis.
Science behind this experiment:
So, you dip a string into a solution of sugar and water and it seems pretty
uneventful. It’s kind of like watching paint dry. How in the world did it turn into a
beautiful crystal of candy on a string?
When you mixed the sugar with the water and then heated and stirred the solution
repeatedly, you created a supersaturated solution. This means there are far more
dissolved particles of solute (the sugar) than the solvent (the water) can normally
dissolve and hold at a given temperature. By stirring the sugar in hot water instead
of room temperature or cold water, the sugar is dissolved faster in the fast moving
(heated) water molecules. As the water cools, the huge amount of sugar particles
remains in solution (a supersaturated solution) and it contains more sugar than can
stay in the liquid. The sugar falls out of the solution as a precipitate (particles).
These connect with other sugar particles, and a crystal begins to grow.
You gave the suspended sugar paticles a great place to begin crystallizing when you
dried some crystals onto the string ahead of time. These are “seed” crystals. As sugar
particles begin to settle (the precipitate), they join and form crystals quickly with
other sugar molecules. You see this crystallization on both the bottom and sides of
the jar as well as on the string. Sugar molecules continue to settle and crystalize on
the string and on top of other sugar molecules until you pull it out of the solution
and enjoy the candy.
Pictures:
Source of lesson:
https://www.stevespanglerscience.com/lab/experiments/homemade-rock-candy/
