Mystery Substance Lab

This week the students worked to figure out a mystery substance. They were given trays with nine different identified substances and one mystery substance that was a combination of two identified substances. They added water to the mystery substance and recorded what happened. Then, they were instructed to try 11 different combinations of the identified mixtures and recorded what happened when they added water. The goal was that they would be able to use their results to identify the mixtures in the mystery substance. It was interesting to see how the students choose which compounds to test. Most were fairly haphazard, but a few did have a system. Some groups inadvertently tested the same combination twice. Others tried a few combinations before deciding that the best course of action would be to try a combination of an identified compound and the mystery mixture. We tried to steer these groups back to different combinations by asking them to explain their reasoning, which only worked with about half of the groups. The other interesting thing was that many of the students wanted to quit if they found something that made the same type of bubbles, even if they hadn’t gotten to 11 yet. We encouraged these students to try a few more by telling them that we weren’t quite sure what was in the mystery compound, so we couldn’t tell them whether their answer was right or not. After all of the groups got to 11, we discussed which compounds they had identified as possibilities. They were all amazed to hear that there wasn’t just one combination that produced the same type of bubbles as the mystery mixture. This led in to the next worksheet, which listed seven specific combinations for them to try. They were instructed to complete the worksheet while paying special attention to the numbered wells they were using. It was important that they match the well number to the combination listed on the worksheet because they were going to look for changes that occurred after the substances dried. However, I estimate about half of the groups went about their merry way without any regard to the numbers. They were good about recording the immediate reaction as it occurred, but they were certainly going to be lost the next day. One group did realize their mistake and corrected the numbers on their worksheet, but that only happened with that one group. Because we wanted all of the students to be on the same page, Ms. Cochran and I made additional plates at the end of the day. This isn’t the first time students have had a hard time following what seem like simple directions and I’m sure it won’t be the last. I’ve seen similar problems when I’ve taught undergraduates, so I know it isn’t just an eighth grade thing, either. Is some way to communicate directions more effectively? It seems like saying, “Your tray has numbered wells. Make sure you match the reaction number on the worksheet to the well number” or “Today we will discuss what belongs in each section of a lab report. There is also a handout posted on our class website outlining what should be in your lab report” should be simple enough. What have you tried in an attempt to get your students to follow directions?


About Sarah Schmidt

I am a PhD candidate in the Ecology & Evolutionary Biology department at the University of Kansas. I study prairie rivers and I am especially interested in algal communities and using lipids to explore food webs.
This entry was posted in 2011-2012 GK12, Uncategorized. Bookmark the permalink.

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