Rock candy is created from a growth of sugar crystals. These crystals form as the solvent evaporates. It is a simple activity that even young children can do, but does take time for the evaporation to occur. This makes it ideal to do near the winter holidays since the air tends to be drier.
Materials and Supplies
- 3 small Petri dishes or shallow aluminum pans
- ½ cup water
- 1 cup sugar
- measuring cup
- small saucepan or beaker
- small spoon for scooping sugar
- wooden spoon
- stove top or Bunsen burner
- magnifying glass
Steps to Make Rock Candy
- Pour the water into the small saucepan or beaker. Add the sugar one small spoonful at a time; stirring with the wooden spoon each time until the sugar completely dissolves. When the sugar will no longer dissolve no matter how much the solution is stirred the solution is saturated.
- Put the saucepan or beaker on a low heat for a few minutes.
- Remove the solution from the heat and add more sugar one spoonful at a time, stirring after each addition until the sugar completely dissolves.
- Pour any remaining sugar into the solution and heat slowly until all sugar is dissolved. Bring it all to a boil then continue to boil for one minute. Pour the solution into the shallow dishes while it is still hot.
Observations During the Steps
- Have students record how many spoonfuls are added to the water before the sugar no longer dissolves.
- Students should write down what happens to the undissolved sugar crystals as the solution warms.
- Have students record how many spoonfuls are added to the warmed water until the solution is saturated.
- The solution should be clear while hot. Have students watch the dishes as they cool and record weather they notice any changes. If the solution becomes cloudy students should look closely at it with a magnifying glass to look for crystals.
Watching the Crystals Grow
Set the dishes in a location that will not be easily disturbed but still allows students to view the daily progress of the rock candy. Each day students should carefully break the crystalline surface that forms so the water can continue to evaporate. Students can also record their observations of the crystal growth, using a magnifying glass to get a closer look.
To create the classic rock candy stick place a coffee stirring stick into the solution shortly after it has been poured into the dishes. The crystals will form around the newly introduced straw, thus forming a stick of rock candy. This works best if the solution is poured into a small glass jar instead of shallow dish, but will take longer to form.
To make colored rock candy add a few grains of colored sugar to the solution shortly after it has been poured into the dishes. As with the stick, the sugar crystals will be attracted to the newly introduced sugar because of its supersaturated state and add color to the crystal formation.
Making rock crystals in the classroom introduces students to the ideas of solutions, solutes and solvents, crystals, the effects of evaporation and material properties. It can also be a fun way to encourage students to be patient while observing what happens in an experiment over a long period of time .
Reference: Cobb, V. Science Experiments You Can Eat. NY: HarperTrophy, 1994.
 |
 |
