What did you do in school today?

October 31, 2006 at 2:35 pm (Teaching)

Heh. I got to have a pretty fun day at work today. Tuesday, I spend all day in the science lab. Since I service kids in each of the three sixth grade classes, I’m able to use this time as “ELA” services, since I’m helping them write their lab reports. Today’s experiment was especially fun.

The students were given six solutions: water, salt water, vinegar & salt, lemon juice, orange juice, and Taco Bell mild sauce. They were given 18 filthy pennies. These puppies were green! After separating the pennies into 6 “cleanliest”, 6 “dirtiest” and 6 in the middle, the students put on of each into the liquids to see which would clean the best.

Can you guess which ones worked the best? My hypothesis was the hot sause. (I do a lab report along with my students to “model” how to fill them out correcly.) Although Taco Bell’s goodness did get it somewhat cleaner, the vinegar & salt was the clear winner, with lemon juice a close second.

I also was asked to do a side experiment, while the other kiddos were working on cleaning pennies. I took a large container, filled it about half way up with vinegar & salt, threw in the pennies from the first class’s experiments, and added a single iron nail. The nail has been in the solution all day now, and it has been bubbling like crazy. What happens (according to the lab director) is that the vinegar strips the copper layering off the pennies, leaving the negatively charged copper ions floating in the solution. They are attracted to the positively charged iron ions in the screw, and start to coat the screw. When I take out the screws, you can see a copper coating on them. The bubbling is caused by the vinegar stripping away the top layer of the iron. The pennies are staring to look black.

Very cool.

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