Daily Chemistry

This year I am trying to immerse my students in chemistry thinking and learning right from day one. There were only two days of classes this week, and the first day had shortened periods, but I still managed to jump start their thinking about chemical reactions, and have a lot of fun at the same time.

Day one involved passing out papers, textbooks, and other administrative duties, but there was still enough time to go outside for the Mentos and Diet Cola demonstration. First I asked students (sophomores and juniors) if they remembered the difference between physical and chemical changes, and how they might tell one from the other when watching chemicals react. Once we had reviewed the difference I placed a 2-liter bottle of diet soda on a table. Then I took out a package of mint Mentos and a large test tube.  The Mentos fit perfectly in the test tube, which I then invert over the opening of the soda; they slide right in quickly.  Students often confuse the gusher that results with a chemical change because there was a "gas produced", so there follows a discussion of whether it was already there or if it was created.
To assist with the discussion I talk about putting a raisin into ginger ale (the bubbles attach to the wrinkles and cause the raisin to float) and explained how the mint Mentos is rough, there are tiny divets all over that the carbon dioxide attach to.

The second day our demonstration was a chemical reaction: vinegar and baking soda.  For this I funneled baking soda into a soda bottle, inserted a baggie which I held around the nozzle while I filled, Let the bag drop onto the baking soda, quickly corked with a rubber stopper, shook and let shoot.  I tried it in the classroom the first period but that proved a bad idea as the foam and cork hit the ceiling and sprayed over a bunch of us in the front of the classroom.  After that I did it out of doors. The trick to this demo is knowing when to let go and not waiting until the pressure forces your hand (in which case it sprays all over you). The discussion that followed back in the classroom was a simple review of acids and bases and how we knew that a chemical reaction had occurred. The chemical equation was written on the board and I pointed out how they were going to learn how to read and write chemical equations plus how to figure out the best ratio of chemicals so there was no excess. 

Such a fun short week. The students were great and I am looking forward to working with them.

2 comments:

thunderroamer said...

I normally do both of those labs. What about the mentos outer shell being eaten when you drop it in the soda?

Reflections of a Science Teacher said...

Interesting. I have not tried this and now will have to do it.