Grow Your Own Sugar Crystal!

Key Concepts

Materials: 
4 cups        Sugar
1 cup          Water  
1                   Stirring spoon
1                   Paper towel
1                   Glass / jar
1                   Popsicle stick
12 inches Thread / string 
 1                  Pot 

Note 1: As this project requires use of a stove, parent supervision is recommended.  Note 2: If you are planning on eating the sugar crystal, make sure to use clean materials throughout the process and do not set the popsicle stick or thread on a dirty surface. 

Activity Directions:
  1. Add water into the pot and pour in the sugar. 
  2. Place the pot onto the stove on medium heat and stir until the water is boiling.
  3. Take your pot off the stove. The mixture inside should have a syrup-like texture. 
  4. Let the pot with the sugar and water inside cool for 1 minute, then pour the mixture into a jar. 
  5. Loop a thread around a popsicle stick at least twice. Then, making sure to leave at least 4 inches of thread hanging off of the knot, tie a knot in the thread so that it firmly surrounds the popsicle stick. 
  6. Set the popsicle stick on top of the open end of the jar, and use the mixing spoon to push the thread down into the sugar solution
  7. Cover the top of the jar with a paper towel
  8. Wait 4 - 7 days. 
  9. Uncover the jar and slowly take out the thread by lifting the popsicle stick. Notice the sugar crystal growing on the thread!
  10. You can eat the sugar crystal right away, or you can let it dry overnight and store it in an airtight container if you want to save it. 

Discussion Questions & Science Explanations:
  1.  Is the sugar water a solution or a mixture?
    1. The sugar water is a solution, because the sugar is dissolved throughout the water and cannot be separated out with a filter. Specifically, the sugar water is a supersaturated solution. 
  2. Why is the sugar water supersaturated? 
    1. When you first mix some sugar into water, at some point the sugar will stop dissolving into the water. This water is fully saturated, because it cannot have any more sugar mixed into it without sugar falling to the bottom. When you heat the water, more sugar is actually able to dissolve into the water. As the solution cools down and its temperature drops, it then becomes supersaturated. This is because the water contains more dissolved sugar than there normally could be at that temperature. The solution is now a little bit unstable. 
  3. Why do the crystals grow on the string?
    1. Because the supersaturated solution is unstable, some of the sugar does not want to continue to be dissolved. The string inside the solution provides a place for the sugar to solidify.
    2. As we all know, water naturally evaporates and becomes a gas. If you’ve ever noticed that you have to keep watering indoor flowers every few days, you are noticing the process of evaporation! Water at the surface changes from a liquid to a gas and is released into the surrounding air. As the water in the solution evaporates, the sugar originally dissolved in it will solidify and collect on the thread inside the jar. 
  4. Was this a chemical reaction? And if so, why?
    1. A chemical reaction occurs when the molecular bonds of a substance change. Dissolving a substance into another substance, in this case dissolving sugar into water, isn’t a chemical reaction because the substances are still the same. We began with sugar and water, and we ended up with just sugar and water. Some common examples of each reaction type include: burning wood (chemical), cooking an egg (chemical), iron rusting (chemical), ice melting (physical), cutting paper(physical), mixing play-doh (physical). 

Additional Experimentation:
  1. If you have a magnifying glass or a microscope, try examining the crystal under a microscope. What parts of the crystal look the same? What parts look different? 
  2. Instead of using sugar, try repeating the experiment with salt. Do salt crystals form as well? How are they the same and different from sugar crystals?
  3. Before leaving the jar to sit for 4 - 7 days, drop some food coloring into the water. Does this change the crystal in any way? ​
Suggested video: https://www.youtube.com/watch?v=tbu-egineUo

​Published 6.5.2020

Author: Alex Zhang