Rock Candy Crystals
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Biology In Elementary Schools is a Saint Michael's College student project from a course that ran between 2007 and 2010 and fully described in this book chapter. The student-created resources have been preserved here for posterity. Link under 'toolbox' for printer-friendly versions of the exercises. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.
Rock Candy Crystals
Student worthiness
Tested and Reliable
Primary biological content area covered
Students will have the opportunity to create their own rock candy while exploring evaporation, saturation (and super saturation), as well as phase changes.
Materials
- Wooden skewers or popsicle sticks
- Food coloring
- Table sugar
- Water
- Cotton string or yarn
- Two hot pots
- Paper cups
Handouts
- Students will make a chart to track the growth of the rock candy over time. They will measure how much the rock candy has grown each day and draw a picture of what it looks like after measuring. They will use these numbers to create a graph when the process is complete.
Description of activity
Students will be introduced to the concepts of saturation (super saturation), evaporation, and phase changes. Each student will be given a paper cup, popsicle stick or wooden skewer, piece of string, sugar, and boiling water in order to create his/her own rock candy. Students will be able to chart the progress of the growth of their rock candy over time and use their data to create a graph.
Lesson plan
The students will begin by being asked if they have ever had rock candy or have any idea how it is made. The teacher will then explain what goes into the making of rock candy--here, evaporation and supersaturation will be explained. The water should already be boiling with the sugar in it (until the mixture is supersaturated), then each student will receive a small cup (about 1/3 full) of the solution. The students will then add two drops of food coloring to their solution and the popcicle stick with a dangling string that has been soaked in water and coated with sugar will be placed in the cup. The cup should then be left in an area that will be undisturbed and (if possible) in sunlight. Each day the students can check the progress of their rock candy formation and add their observations (drawings of their cup/rock candy) to a chart.
Potential pitfalls
Some of the potential pitfalls that we ran into while running this were:
- Students were disappointed that they could not eat the rock candy in the end due to how sanitary the beaker the water was boiled in was; therefore, using a regular (sanitary) pot to boil the water would be a better option to consider or the teacher could choose to bring in store bought rock candy.
- Students will become impatient waiting for the rock candy to form, therefore it might be good to have a worksheet of some sort to go along with the activity that explains the process.
- We were not sure which method to make the rock candy worked the best--either putting the popcicle stick right into the cup, or dangling a string from a popsicle stick into the solution--so it might be a good idea to try both ways from the start to see which works best for you.
Reflection--
The students seemed to really enjoy this experiment because it seemed that candy was something they could relate to at such a young age. They really liked that they were going to be able to eat the end product at the end, as well. Offering different ways to track the growth, such as writing observations or drawing what it looked like was also a good idea because some of the students were not native english speakers. This was an experiment that many did when they were growing up, and it is pretty simple and a good way for them to learn more about evaporation and supersaturation.
Math connections
Since the crystals will not form instantly, students can track and measure the progress of the growth each day by using a chart. They can measure this progress through drawing what they observe happening. In the end the students can compile their data and create a class graph. This also allows for students to artistically express what they are observing, tying art into the activity.
Literature connections
Here is a list of possible literature resources to have avaliable in the classroom to either introduce or compliment this experiment,
Cobb, Vicki, 1984, "Science Experiments You Can Eat", Harper Trophy. This book includes an example of another verison to grow rock candy crystals along with other edible experiments that might spark students interests and lead to further learning opportunities.
Gordon, Donald R.,2006, "The Rock Candy Bandits", Trafford Publishing. A great book to read during meeting time, telling the story of detectives trying to solve the case of who stole the rock candy.
Hall, Judy, 2003, "The Crystal Bible: A Definitive Guide to Crystals", 2003. A great extenstion book for this activity introducing students to the different forms and types of crystals.
Levine, Shar, Leslie Johnstone, and John Manders, 1999, "The Incredible Secret Formula Book", Troll Communications. This book includes a verison of creating your own rock candy crystals along with other activities for students to create.
Morrison, Phylis and Alan Holden, 1982, "Crystals and Crystal Growing", MIT Press. This book introduces students to the form and shape of crystals.
Squire, Ann O., 2002, "Growing Crystals", Childrens Press. This book introduces students to the form and shape of crystals.
Symes, R.F and R.R. Harding, 2007, "Crystal and Gem", DK Children. This book introduces students to the form and shape of crystals.
Connections to educational standards
7.2 Investigation Students design and conduct a variety of their own investigations and projects.
a. Design and conduct an experiment (a“fair test”);
b. Design and conduct a systematic observation;
e. Plan and manage a schedule;
7.3 Theory
Students understand the nature of mathematical, scientific, and technological theory.
b. Look for evidence that explains why things happen;
c. Modify explanations when new observations are made or new knowledge is gained.
7.12 Matter, Motion, Forces, and Energy
Students understand forces and motion, the properties and composition of matter, and energy sources and transformations.
b. Observe and describe changes of states of matter (e.g., in water);
Next steps
This could be used as an introductory lesson into further lessons (or unit) about crystals and crystal formations. There are numerous books (see literature connections) that can introduce students to the shapes, sizes, and colors of crystals.
Students could deconstruct their rock candy crystals once they have formed and inspect them under either a microscope or magniying glass and draw what they observe, being able to observe the shape of the individual crystals that have formed.
This lesson could also tie into a future lesson about the water cycle.
Citations and Links
http://candy.about.com/od/hardcandyrecipes/r/rock_candy.htm
http://www.exploratorium.edu/cooking/candy/recipe-rockcandy.html
