I talked to them about what was taking place during this reaction. NaCl and CO2 are both examples of matter and matter takes up space. When the salt is added to the soda, it pushes the bubbles of carbon dioxide out of its way. These bubbles rise to the top bringing small amounts of the flavored water (soda) with them. This movement of the gas forms the foam on the top of the liquid. Replacing a gas with another substance is called effervescence. In other words, effervescence is created by dissolving a gas in a liquid and then adding a soluble solid (salt).
As I explained this to the munchkins, they came up with their own experiment question, “What about sugar then? and flour? Will they make the soda foam up too?” “Let’s find out!” I replied. Indeed, sugar worked! We didn’t have enough soda (I didn’t want to open another can) to test other solids .. but I promised them we could continue this experiment again.
What intrigues me about this activity is that it is one that is frequently found in science experiment books for children, like Janice VanCleave’s Chemistry for Every Kid. While these books are excellent introductions to science … they are not considered true INQUIRY by science standards. The National Science Education Standards (NSES p.23) defines scientific inquiry as “the diverse ways in which scientists study the natural world and props explanations based on the evidence derived from their work. Scientific inquiry also refers to the activities through which students develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world.”
The activities in these books are great hands-on activities that help to demonstrate key scientific processes or concepts yet they are not true inquiry. This is one of my biggest pet-peeves or frustrations with curricula and books targeted for parents. Parents must use caution, therefore, when considering these for use in science fairs. However, most of the activities can easily be adapted or modified … by applying inquiry processes … to achieve the goals and standards set by NSTA and/or the state benchmarks.
I’ve always said that if the student can phrase their experimental question, to fit the pattern: How does ________ affect ________ ? then they are all on their way to developing a successful inquiry project that will do well in a traditional science fair.