Making Rock Candy

Making Rock Candy Discussion

rock candy  This is an experiment in controlling crystal growth. Rock candy, like most candy, is made primarily from sugar. The candy can be anything from large single crystals to an amorphous solid. In this experiment you will produce each end of this spectrum.

Making fudge is an excellent follow-up to this experiment. The key to making good fudge is controlling crystal growth in a supersaturated solution. Most fudge recipes use both chemical and mechanical means to reduce the size of the sugar crystals in order to have a creamy texture. An analysis of fudge recipes will extend the appreciation of how chemical principles are used in candy making. You may wish to make fudge at home and have your family evaluate your results.


To make sugar crystal rock candy.


cane sugar, small sauce pan, pencil, weight (a paperclip will do), string


Do not eat any part of the candy made during this lab. Use safety precautions while heating the water.


1. Boil 1/2 cup of water in a very clean saucepan. Turn off the burner.

2. Add sugar until no more sugar will dissolve. Be sure that all the crystals have dissolved. It may be necessary to re-heat the solution. You may wish to use an internet search engine and look for recipes to make rock candy. These recipes will give you other ideas of things that you can add to make your rock candy unique.

3. Tie a weight on a piece of string. Suspend the string in the supersaturated sugar solution using a pencil to support it.

4. Place the pan where it will not be disturbed for a few days. The longer you allow your solution to sit undisturbed, the better your results will be. Make and record daily observations of crystal growth.

Think about the following questions.

1. What type of solution did you prepare?

2. What happened to the solution as it began to cool off?

3. What caused the solution to crystallize?

4. What do you think would happen if the solution was stirred or jostled during the days it is forming?