Today’s lab, Clock Reactions, is actually from the high school curriculum, Modern Chemistry. It starts out talking about time-released medications and how to change the rate of reaction of medicines (their digestion). So I asked the students, “What could you do to change the speed of a chemical reaction?” They answered with changing the temperature or the concentration of the chemicals, pH and surface area. This lab has students drop effervescent antacid tablets into 15ml of water and record the time it takes for the reaction to take place. Instead of just watching the reaction, students listened to the fizzing sounds it makes (producing gas) and didn’t stop the timers til the fizzing sound stopped. They did this 1/4, 1/2, 3/4 and 1 whole tablet in cold water and most of them found the reaction took longer than 5 minutes at which point I told them to stop because we were going to run out of time. They were supposed to repeat the whole experiment for room temperature and hot water as well but we were going to run out of time and tablets if kids did all of them so we just did 1/4 and 1/2 tablet for room temperature and hot water. As expected the reactions went faster in the hotter water. Molecules are moving faster and therefore bump into each other more often and are more likely to react. They also ground 1/4 and 1/2 tablet into powder with a mortar and pestle to see if increased surface area would speed up the reaction and it definitely shortened the reaction time.
This lab was pretty good but asking the students to do 3 temperatures for 4 different tablets sizes was too much. They should have just done that at one temperature so the only thing they changed was how much tablet went in the water. Then pick one tablet size, like 1/2 of a tablet, and see how water temperature affected the reaction time. Finally ground up the same size table and observe its reaction. Trying to measure all these reactions for 4 different tablet sizes made it overly complicated and made it more difficult to see exactly what was happening. The other thing I would change is having more jars around to put the centrifuge tubes in. The tubes have flat bottoms but quite a few got knocked over today and being able to place them in a small mason jar usually keeps that from happening. The lab also has students do the experiment with 0.1M HCl but since this was my middle school class, I skipped that part, which from the number of spills we had today…was a good idea.