Tuesday, January 27, 2015

The Great Squid Challenge

One of the things I love about gas laws is the possibility for inquiry labs.  I start with the conceptual understanding of the relationships between gas pressure, volume, temperature and number of gas particles.  Kids can usually predict the relationships between any two of these four properties; I use this PheT simulation to help them see these relationships after they make predictions.  Then we are ready for a lab.

Students bring a plastic bottle to class on the day of lab.  I save bottles at my house and dig through the school trash and recycling bins for kids who forget.  The Great Squid Challenge has two parts.  First students must use a kit to create a working cartesian diver.  I show them a sample, but give them no extra instructions.  I tell them that instead I will give them the pleasure of figuring it out.  Once everyone in the lab group has a working squid, they have a slightly harder task.  Given a bottle and 5 numbered and weighted dropper bulbs, the students must make the droppers fall to the bottom of the bottle in numerical order.

It's great fun to watch the students tackle these two jobs.  They begin with doubt about how they will create the squid.  Some quickly assemble the parts but squeeze with all their might and still can't get the squid to dive.  Then they have to tinker until they get it right.  Eventually, the pieces all fall into place because once they get the five numbered droppers, they usually achieve that task fairly quickly.

In this picture at the left, you can see this group is systematically filling the droppers and laying them on the table before they test them in the bottle.  Many groups cheer and high-five when they succeed.  Only one group out of 30 did not finish during class this year.  

The day after this lab, I ask them to explain how the squid works on a quiz.  The students have to tell me which gas properties are constant, which properties change, and which gas law can be used to explain the experiment.  Most students did an excellent job at explaining this, demonstrating a solid understanding of the concept.

We buy our squid kits from Steve Spangler Science.  They also sell a kit where one squid hooks a second one. I have never tried that one, but it looks like big fun.  I bought some brass hardware and plastic droppers to make the numbered dropper sets that I reuse every year.

When I compare this to other gas law labs - like the one where you stack books on top of a syringe to increase pressure and measure volume - the payoff here is much greater.  Students really like this experiment.  The risk is low because the materials are very safe and the success rate is very high.  The materials are not very expensive.  Best of all, students understand and can explain the concept the next day, so they are still applying the relationship between two gas properties and the law that defines it.

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