Rock Candy Experiment

**This experiment requires the help of an adult**

For this experiment you will need the following:

      • 6-inch piece of string

      • A pencil

      • A paper clip

      • 1 cup of water

      • 2 cups of sugar

      • A glass jar (Any type of jar will do, but pint-sized canning jars work well because they will endure the hot temperatures. Tall, skinny olive jars also work well because they don't require as much liquid.)

Directions

  1. Tie the 6-inch piece of string to the middle of the pencil.
  2. Tie the paper clip onto the end of the string.
  3. Lay the pencil across the top of a jar so that the string hangs down the middle of the jar.  If it hangs down too far, roll the string around the pencil until the string is not touching the sides or bottom of the jar.  
  4. Now that the string is at the right length, remove the string and pencil from the jar and put them aside.
  5. Get a helpful adult!
  6. Pour the water into a pan and bring it to a boil.
  7. Pour about 1/4 cup of sugar into the boiling water, stirring until it dissolves.  
  8. Keep adding more and more sugar, each time stirring until it dissolves, until no more will dissolve.  It will take longer for the sugar to dissolve each time, so don't give up too soon.
  9. Have an adult carefully fill the jar with the hot sugar solution.  
  10. Submerge the paper clip and string into the sugar solution.  Make sure the string hangs down in the middle of the jar.
  11. Allow the jar to cool and put it where it will not be disturbed.

Now just wait. The sugar crystals will grow for the next few weeks.

Tips:

  • Crystals will form on a cotton or wool string or yarn, but not on a nylon line.  If you use a nylon line, tie an already-formed crystal to it to stimulate the growth of more crystals.
  • If you are making the crystals to eat, do not use a fishing weight to hold your string down.  The lead from the weight will end up in the water; lead is toxic.  Paper clips are a better choice.

Why it Works

When you mix the boiling water and sugar you make a super saturated solution. This means that the water can only dissolve the sugar if it is very hot.  As the water cools, the sugar "un-dissolves" and becomes sugar crystals on the string. The string and paper clip provide something for the crystals to start growing on; they acted as a “seed.”  As the water evaporates, sugar crystals form on the string, and the shapes that they form reflect the shapes of the individual sugar crystals.

Experiment

Try adding food coloring or flavoring to the sugar syrup before making the rock candy.