This is from last fall, shortly before I left my previous position, when I was *finally* able to do an in-person STEM program for the first time in a year and a half! Things were too hectic at the time to write it up due to job hunting, interviews, and moving, but things are slightly calmer now. Unfortunately, I did not get many pictures from this program.
I kept this program really simple due to not having a lot of time to plan and prep because of understaffing and not really expecting a big turnout for the first program after not having any for so long. So instead of 2-3 activities, I just kept it to one. This program fell during the month of our community read, and I was asked to have at least one program from each age group to tie in with it. The community read for adults was a cookbook (an odd choice for a community read if you ask me, which they didn't), and the one for kids was a "kitchen chemistry" type of book, with science experiments related to or using food, which was right up my alley.
I decided to do the activity of using yeast to blow up a balloon to demonstrate how they produce CO2 (carbon dioxide) gas, which is what makes bread dough rise and leaves all the little holes in the bread, and to make it a true experiment we would test different water temperatures to determine which one was optimal.
Time: 1 hr
Budget: $10 for up to 20 or so kids
- baker's yeast (you can buy a 1 lb bag from Amazon for the same price as a few packets at the grocery store, and less than a 4 oz jar)
- water of various temperatures
- latex balloons
- 16 oz plastic bottles with narrow neck
- 1 c liquid measuring cup
- measuring spoons (1 T, 1 t, 1/2t)
3. Add 1/2 t sugar to each bottle (in hindsight I realized we should have used a whole teaspoon).
I brought this to the kids' attention, and asked them to observe the balloon as well as the growth in bottle compared to the others. They quickly observed that there seemed to be much more growth and activity as compared to the others, yet the balloon was not inflated as much, and that this did not make sense. I asked them what they thought the explanation could be, and they thought a minute, then quickly hypothesized that the balloon had a leak. I asked how we could test that, and they said try a new balloon.
From this, we concluded that 90 degrees was the optimal temperature (of the temperatures tested) for yeast growth and CO2 production, but that yeast could survive and grow at room temperature (around 70 degrees F) as well, but more slowly, and that yeast could not grow at near boiling temperatures. Another interesting observation was that as the bottle with the near-boiling water cooled, the balloon actually inverted and became sucked inside the bottle, which gave us an opportunity to talk about the properties of gases and gas laws; how the molecules have more energy and spread apart at higher temperatures, but lose energy and condense at lower temperature, decreasing the pressure and creating a vacuum in a closed system.
Though I didn't think this was necessarily the most exciting experiment, the kids that participated really enjoyed it and were very engaged. It was a good lesson for me that sometimes a single activity more thoroughly investigated and discussed is enough, maybe even better, than rushing through multiple activities. The turnout wasn't great, about 8 kids and a couple of adults, but that wasn't surprising since we were just getting started back with in-person programming, and unfortunately the older kids really weren't coming to the library like they used to.