Welcome back for one of our most exciting lesson's yet! Our last science lesson introduced the concept of chemical reactions. This time, the 4th and 5th grade students were elated to explore a physical reaction- rock candy!
Examples from the kitchen are a great way to explain physical versus chemical reactions. During this lesson I used the example of toast to compare to our rock candy in order to decide; is it chemical, or is it physical? Making toast is a chemical reaction due to the rearrangement of molecules during the toasting process. Bread can be turned into toast, but toast can't turn back into bread! Our rock candy is an example of a physical reaction. Why? The sugar dissolves, but does not disappear or form a new substance in conjunction with the water.
Before the kids arrived for the day I prepared a super saturated solution of sugar and water along with a plate of sugar to roll our candy sticks in. This is done in order to make sure the crystals form on the stick.
Before jumping into our lesson, we watched a brief cooking demo. After the demo I introduced a few new definitions to our STEAM adventures with the help of our students.
In this experiment, our solute was the sugar and water was the solvent. Why is a review of the term evaporation important to this physical reaction? As the water evaporates, it will cause the super saturated solution to become even more saturated; therefore helping the crystals grow!
Each student received a glass jar with their name on it for their rock candy. Students were given half a skewer to roll in sugar with teacher assistance. After each student received super saturated solution, they were given the choice to add two drops of food coloring. The skewers were then clipped with a clothespin at the top of the jar, leaving 1" of space between the stick and the bottom of the jar.
The students waited patiently with excitement for the rock candy to grow over Spring break. It turned out we had to wait a few weeks after since the process took longer than we initially thought. The students were elated to reveal their rock candy! They did not turn out as crystallized as we thought, but the students were still excited to eat it.
ElayJaih proudly shows off her rock candy.
While the students were munching on their candy we discussed reasons why it did not turn out fully crystallized. These included vibration, boil temperature of the solution, air particles; just to name a few. If we performed this experiment in the future, I would adjust the boil temperature of the super saturated solution, or cover the jars with wax paper.
Clockwise from left: Kiyanah, ElayJaih, and Edwin enjoy their science experiments.
While the students were munching on their candy we discussed reasons why it did not turn out fully crystallized. These included vibration, boil temperature of the solution, air particles; just to name a few. If we performed this experiment in the future, I would adjust the boil temperature of the super saturated solution, or cover the jars with wax paper.
Lastly, dumping the solution from the mason jars revealed a cool "sugar cave"! Some chose to eat this part, others just marveled at the crystals.
Rock Out!
- Anna
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