This week in Science & More we looked at Carbon Dioxide three different ways - we created it, we watched it, and we changed it.
I asked the kids what they knew about carbon dioxide, and they told me that you exhale it. Someone added that trees inhale carbon dioxide.
And so we started with creating carbon dioxide. I had prefilled a balloon with 1 teaspoon of baking soda and added 2 teaspoons of vinegar to an empty 8oz plastic water bottle. I asked everyone what they thought would happen when we put the balloon over the bottle and they were all very sure that it would get blown up. They were really hoping it would inflate enough to pop, but I had made sure to avoid that by not putting too much baking soda and vinegar in such a small bottle. Of course, just as they predicted, when the baking soda and vinegar mixed, they created a chemical reaction that caused the balloon to inflate!
I showed them a diagram of vinegar (acetic acid) and baking soda (sodium bicarbonate) and used Chinese Checkers pieces to model what had happened in the water bottle.
(image found on https://sites.google.com/site/baumannchemistry/unit-8-stoichiometry)
Next, we watched carbon dioxide in action. I asked them if they knew another name for soda. They weren't sure, so I gave them a hint. I told them it had to do with the bubbles in soda. They still weren't sure, so I explained the word carbonated. We filled a cup with ginger ale and added a handful of raisins. We watched as the bubbles of carbon dioxide got stuck on the raisins and carried the raisins to the surface, making it look like the raisins were dancing. I asked why they thought the bubbles were able to carry the raisins, and they guessed that it was because the bubbles were made of a gas that was trying to escape the soda. I asked if they thought that meant carbon dioxide was heavier or lighter than the soda, and they all agreed it meant it was lighter.
Our final experiment was to change carbon dioxide, and it built a bit on the previous Science & More session about acids and bases. On a table were three plastic cups. One had 1 tbsp of vinegar in it, the second cup was empty, and the third cup had 1 tbsp of baking soda in it. I had a bottle of red cabbage juice (directions to make cabbage juice at home are at the bottom of the post), which works great as a pH indicator. I added the red cabbage juice to each of the cups, and we all thought it was pretty cool to see how quickly the juice changed color. We matched the three cups to their place on the pH scale and determined that vinegar is acidic (which made sense since it is acetic acid) and that baking soda is a base. Cabbage juice was determined to be neutral.
(image found on https://www.discoveryexpresskids.com/blog/test-ph-levels-with-red-cabbage)
Next, everyone was given a small cup with cabbage juice in it and a straw. We all blew bubbles in the cabbage juice for about three minutes. I asked them if they thought the juice was changing color or staying the same. At first, it looked like the juice was staying the same color. But slowly people started to see that their cub of juice was turning more pink.
We compared our cups to the color chart and found that the carbon dioxide we blew into the cups was acidic! We then talked a little about how carbon dioxide turns into carbonic acid when it mixes with water, and how pollution and carbon emissions can mix with all the water in the ocean (this is called ocean acidification).
Finally, it was time to play. Everyone got a bottle of water and vegetable oil, and we picked which food coloring we wanted to add. Then we added alka-seltzer to the bottle, and watched the results - Carbon Dioxide Lava Lamps!
Since the bottles were small, we used 1/4 of a tablet at a time. The kids got creative with their colors. Since the drops of food coloring would take a while to drop through the vegetable oil, they figured out that by adding a piece of alka-seltzer, they could mix the colors into the water much quicker! Everyone recognized that the alka-seltzer tablets released carbon dioxide bubbles just like the soda had, only instead of taking raisins to the top, they took colored water! Everyone was able to take their lava lamps and a packet of alka-seltzer tablets home.
There are several different ways to make Red Cabbage Juice Indicator:
Cold Water (directions from PBS Kids' Zoom)
Blender (directions from Steve Spangler Science)
Boiling - this is how the indicator juice for this week's Science & More was made (directions from How Stuff Works)
A word of warning when making this by blender or boiling - it smells pretty disgusting, and the used cabbage leaves will look very strange!