Wednesday, July 24, 2013

Expanding Molecules or How we nearly set fire to the Microwave.

We found the Accidental Scientist: Science of Cooking site while we were doing our Cookie Unit study. There is a lot of great information on this site but what caught Miss K's attention was an activity to make 'Monster mallows'. She saw it as a great reason to buy candy, I saw as a way for her design her own experiment.

Instead of just observing a marshmallow heat for one minute in the Microwave Miss K chose to heat  marshmallows for  varying lengths of time so she could compare the changes. 

We found some cute retro style marshmallows at Target selected 4 to test and put the rest aside for consumption.

Using a sharpie Miss K labeled our test candy 1 to 4, these was the method she wrote:
1. Heat for 30 seconds
2. Heat for 60 seconds
3. Heat for 90 seconds*
4. Left out on the counter (control)

What happened?

I wish I had taken a video of the marshmallows, the kids reaction and their later dramatic retelling of it all to Daddy! As promised by the Accidential scientist all the marshmallow's puffed up dramatically during heating! The kids were amazed at how big they got! What did differ between heating times was the final texture and color of the candy (which we observed AFTER it cooled down).
After 30seconds the marshmallow nearly quadrupled in size during heating. When no longer being heated it begans to shrink to approximately double its original size and was still sticky.

After 60 seconds the marshmallow has not only quadrupuded in size but collapsed again and browned a little around the edges. When it cooled to the touch it felt hard on the outside but remained sticky at its core.

We only made it to 75 seconds with marshmallow #3 before it began to seriously spark and smoke. At this point I stopped the microwave and ran the blackened candy outside so it didn't set off the smoke detectors. When it cooled down we got to observe the changes. There was no stickiness, it was very brittle and the burnt sugar was very dark and shiny.

Why did this happen?

Candy is primarily full of sugar. In the case of Marshmallows there is also a lot of air and water. When you heat something in the microwave the water molecules vibrate at a crazy speed. This heats up the water and sugar molecules and air bubbles.  The air bubbles push against the walls of the now softened sugar and the marshmallow blows up like a balloon.
When the heat is removed the marshmallow begins to cool and the air bubbles shrink and the sugar hardens. If  you continue to heat  an already 'puffed up' marshmallow it will eventually get so big it  'pops' and deflate.

What did we learn:

My Mother can attest to the fact I do not have a great track record with Microwave ovens.
In my teens I decided to make popcorn in the microwave using a pyrex dish, gladwrap and oil. Yes oil! Lets just say my Mum was not happy to come home to a microwave with a blackened interior complete with popcorn shaped groves...again sorry mum! For some reason Dad didn't seem surprised.

In hindsight this was probably not a great experiment for us but it was a great lesson in the effect heat has on molecules! It also inspired us to look for some more ways we can use food to teach science concepts. Here's our collection of things we want to try!