Saturday, August 10, 2013

Rock Candy

Kids love candy, I mean what kid doesn't? So how could I make candy part of a learning experience? Well a few good ideas came to mind, but the one that stood out the most was Rock Candy.

Rock Candy is fun to make because you don't get instant gratification, instead over time you see these crystals growing out of seemingly nothing into this beautiful yet seductively sweet prize, and the kids have learned about Chemistry and Earth Science without even knowing it.

To make rock candy you need a good amount of sugar, roughly 1 lb for every 2 cups of solution, this is because you need to make what is called a super saturated solution.
In Chemistry we learn that all solvents, things we dissolve other things into, have a point at which they can no longer dissolve the solute, what we put into the solvent to dissolve, when this happens it is called a saturated solution.  However, to go from a saturated solution, to a super saturated solution we need to temporarily change the solubility, how well the solvent can dissolve the solute, we do this in a sugar/water solution by raising the temperature of the water to boiling. Once the water boiling we continue to add sugar until it can no longer dissolve the sugar, leaving us with yet another saturated solution. As the sugar/water solution cools to room temperature the water's solubility returns to its original proponents, creating a super saturated solution.  The excess dissolved sugar has no choice but to revert, meaning change back, into crystal form; in chemistry we call this process precipitation, and the crystals the precipitate, what has come out of the solution in solid form.
This crystal formation is where we bring in some really fun Earth Science.  See as the water cools and evaporates the solution begins to be more and more saturated meaning that more and more of the sugar needs to leave the solution. In this attempt to leave the solution they cling to any "seed" material they can, including the sides of the container and your string/stick. As these seed crystals form they attract other sugar crystals to form atop them molecule by molecule.  Your finished rock candy will be made up of roughly a quadrillion, or a million-million, sugar molecules attached to your string/stick. These crystals should be clearly defined in monoclinic crystals, which are crystals with sharp right angles and smooth sides of various sizes. This process is similar to how crystals such as quartz are made in caves today, except this is much more tasty!

Rock Candy

3-5 cups sugar, more may be needed
2 cups water
food coloring, optional
candy flavoring, optional

Seed your string/stick so that crystal formation has a "preferred" place to attach.

If using string: string should be 2/3 the length of intended jar/cup depth. Wet string, roll in sugar, lay flat on a piece of wax paper to dry completely.  Dry time can take a few days, so plan in advance.

If using a stick: no prep is necessary, but seeding provides a better surface for crystal formation.  Wet stick, roll in sugar, allow to dry completely.

Heat the water in the saucepan over medium-high heat until it comes to a boil.
Pour about 1/4 cup of sugar into the boiling water, stirring until it dissolves.
Keep adding more and more sugar, each time stirring it until it dissolves, until no more will dissolve. This will take time and patience and it will take longer for the sugar to dissolve each time. Be sure you don't give up too soon. Once no more sugar will dissolve, remove it from heat. Allow to cool for 5 minutes.
Pour sugar/water solution into your container. If you wish to add flavors and colors now would be the time. Put enough food coloring in the solution, make sure you add enough coloring that the solution is many shades darker than your intended result. Add in your candy flavoring, we used 1/4-1/2 dram of flavoring oil per 2 cup container. Stir well with spoon or unseeded stick.
Gently suspend your stick/string in the solution, try to keep the stick/string from touching the bottom or sides of the container or the crystals will attach the stick/string to the container.
Cover lightly as to not slow down the evaporation process, but to keep out dust.
Place in an area where it will not be disturbed for seven days.

My husband attacked the containers with tape to keep them from moving
Feel free to check your crystal growth over the next few days, but be sure not to disturb the containers! After 7 days you should have sufficient crystal growth, remove from solution and allow to dry. 
Aeries' solution after 14 hours
Safety Note:  When working with the sugar-water solution an adult should be present.  When you heat sugar to super high temperatures it can create some very nasty burns. Be safe and use the necessary safety equipment.

This experiment is still in process, check back later for updates. This is also cross-posted from my DIY page.

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