This is a fun partial lesson in thermodynamics! Honestly, chemical cold packs or homemade ice cream from a baggy are probably better illustrations of thermodynamics, but I just wanted a semi-acceptable reason to make pop rocks with my kids…So, thermodynamics it is.
In this experiment, we will be observing an endothermic process, which is a reaction when the system absorbs energy from its surroundings in the form of heat. (The opposite would be an exothermic process which would be a reaction when the system releases energy in the form of heat.)
- 1 cup organic sugar
- 2 teaspoon baking soda
- 1/8 cup plus 2 teaspoons citric acid (We use this one … And yes, I purchased it at Whole Foods. Oh, how I wish I could quit you.)
- 1/4 cup honey
- 1/8 cup water
- 1-2 teaspoons natural flavoring extract (whatever flavor you’d like)
- 1 teaspoon to 1 tablespoon natural food coloring (We use this food coloring which requires a tablespoon of color. However, this is also a good natural coloring which yields a more vibrant color with less product.)
1. Line a baking sheet with wax paper.
2. In a small to medium saucepan, combine the sugar, honey, and water.
3. Cook the mixture until it reaches 300 degrees (measured with a candy thermometer).
4. Remove from heat and let cool to 275 degrees. Then add the 1 teaspoon baking soda, 1/8 cup of the citric acid, flavoring extract, and food coloring.
5. Mix well.
6. Spread the mixture out onto the baking sheet, sprinkle with the remaining baking soda and citric acid, and allow to cool completely.
7. When candy cools, remove from wax paper (it may be initially stuck, but should peel off easily), break into large pieces, place in a well-sealed plastic bag, and crush into small pieces using a rolling pun or meat tenderizer.
*How your homemade pop rocks work:* Check out the side of the broken pieces of candy. You should see holes created from the baking soda where CO2 has been trapped! When you put the candy in your mouth it melts and releases the CO2 pressure and that is the “pop” effect. Also, when the citric acid and baking soda (sodium bicarbonate) coated on the outside of the homemade “rocks” combine with moisture (in this case, your saliva) it creates the endothermic reaction you have toiled in the kitchen to observe!
Here is the chemical equation if you were to mix citric acid, baking soda, and water together:
H3C6H5O7(aq) + 3NaHCO3(aq) –> Na3C6H5O7(aq) + 3CO2(g) + 3H2O(l)
The CO2 (carbon dioxide) gas coming off is what makes the solution fizz.