October 19, 2015
Students always get excited as Halloween approaches. The thrill of collecting treats is real, but as teachers, how can we take a pile of sugar and turn it into a lesson? A really great science teacher trick is to use some of the kids’ treats for a science experiment. Pop Rocks ™ are a really fun candy for experimenting. Not only are they colorful, sweet and loud, they are also bursting with science concepts that can be incorporated into your middle school physical science lesson (or in this case fizz-ical science).
Using “Is the popping of Pop Rocks a physical or chemical change?” as a guiding question, you can address content ideas like the structure and properties of matter and chemical changes while reinforcing science and engineering practices like analyzing and interpreting data, and engaging in argument from evidence.
Have the students brainstorm some ideas about the observations and data that they could use to answer the guiding question. Let them explore any ideas that may “pop” into their head. Some typical examples of evidence of a chemical reaction that they could investigate would be color changes, temperature changes, and the release of a gas.
The students will be eager to taste test their way through the experiment, but the first rule of the lab is that you don’t eat things in the lab. Of course if any one does eat their sample it will be easy to identify the culprit. So what lab tools can students use to model and measure the popping phenomena?
To mimic the reaction that takes place when Pop Rocks are eaten, we used a beaker with water so we could observe possible color changes and a Temperature Probe to measure any temperature change.
After some of the Pop Rocks were added to the water, the solution changed color, and there was the characteristic popping sound.
Surprisingly, the temperature remained constant. In hindsight this shouldn’t have been a surprise since the candy doesn’t make your mouth feel cold, or hot, when you eat it.
So far we still haven’t answered the question that started this investigation— is it a physical or chemical reaction? What is going on, and why is it popping?
To investigate further, we measured the pressure change to see if a gas was being produced. We connected the Pressure Sensor to a one-hole stopper and a small plastic bottle with some water in it. We added the Pop Rocks to the water, put the stopper in place, and started collecting data.
Don’t forget to hold on tight because we’re going to get things popping!
The data doesn’t really explode off the screen, but the pressure did increase a measureable amount - about 4 kPa over a two-minute period.
Once the data has been collected, the science and engineering practices come into play. What does the evidence indicate about the Pop Rocks? Is it a chemical or physical change? You could have the class break up into two groups (Team Chemical and Team Fizzical— the joke never gets old!) to debate the answer based on their findings. Finally, have them do some research on the subject to see what is really going on and have them create a drawing to indicate the process.
And of course, now that you have tricked the students into thinking, learning, and most importantly doing science, you can give them the treat— a pack of Pop Rocks.