Unit 2 Reflections: Diffusion Demos

I feel I'm finally making some progress with my students.  I've said this before-- hopefully I won't end up eating crow this time.  This week started with a state writing assessment that interrupted Monday's classes:  I only saw about half of my students on Monday while the other half tested.  Kudos to my school, though-- I really like how they implemented it this year as opposed to last year.  We only had a single day of interruption, as opposed to an entire week.

The interruption was not a bad thing.  It allowed me to work one on one with a number of students who really needed help, but aren't dedicated enough to ever come to tutoring after school.  I feel like I have more of the class on the same page now.

This unit, I also have decided to reduce lab groups from groups of 4 to groups of 3.  The leaders of our modeling workshop were big proponents for groups of 4.  It also fits really well with the "Lab Roles" sheet they gave us.  However, I think with standard-level students, groups of 3 are much more efficient.  When there are 4 students in a group, there are too many opportunities for the less motivated students to zone out or get off task, even when they are supposed to have a role.  I used groups of 3 with my standard biology class last semester because of the small class size and just told the students that the lab manager is now also responsible for the recorder's role.

On Tuesday, we began Unit 2 ironically by completing "The Model So Far..." for Unit 1.  Students then read a brief article on Democritus' atomic theory and wrote a short response comparing our model to his.  The consensus:  we are thinking like Democritus at this time, but we also know from prior knowledge that Democritus wasn't completely correct.  I gave a little speech about why we are doing this:  since we can't see particles, we need to be able to paint a good mental picture of what's happening with these particles.  And yeah, a lot of this stuff seems basic, but if we have a good model in our heads, we can add to this model just like scientists' added to Democritus' original model.

I am learning that with my current group of students, I have to be extremely clear on what we are doing.  They are literal to a fault and do not "go with the flow" well.  So if they don't 100% understand an activity or a demo before we begin, they shut down.  I've been using a lot of straight forward guiding questions before an activity.

I had them create a page in their lab notebooks that said "Unit 2- Energy & States of Matter" and explained we would be looking at how energy affects the states of matter.  Then I first told them we would be observing how particles move in the gas state.  We talked about what odors are and how our sense of smell works.  I then had them set up a page for the demonstration observation of the movement of Axe Body Spray through the classroom (I didn't have strong enough perfume).  I had them write a guiding question:  How do particles move through gases?

The demo is straight forward:  spray a puff of strong-smelling stuff in the center of the room and have students raise their hand when they smell it.  Also, have them record the order in which people smelled it in their lab notebooks.

After the demo was complete, in new lab groups, I told them to story board all particles involved in the demonstration from the moment I sprayed the Axe until I said stop.  The results were interesting.

Many of them forgot the air, or didn't think it played a role:

Others seemed to just think it was co-existing in the room, but not really doing anything:

And then some groups got extremely creative:

They explained that the particles joined together and started moving all around the room

Misconceptions galore!!!  This is one thing I love about the modeling curriculum.  Diffusion seems like such a basic concept that I've always thought my students understood, but in reality, they had zero clue that the air in the room was a factor.

I led them back on track by giving them the loose analogy of a pool table:

I can rack my billiard balls into a triangle, but what causes them to break?  How do the balls move when the cue ball hits the triangle?  What if I racked my balls, but decided not to play pool today and never shot my cue ball, where would the balls be tomorrow?

From that, they were able to understand that the room air particles were crashing into the Axe particles, causing them to move in different directions than they would on their own and spread throughout the room.  I then told them we call this "diffusion."

I reinforced the idea with THIS simulation on Kinetic Molecular Theory, which shows a red particle getting bounced around in a sea of moving blue particles.  We used this simulation to define "diffusion" as a class.  All the classes came up with something the along the lines of particles being spread out due to collisions between particles.

Next, it was on to how particles move in liquids.  For this, we did a simple demo of food coloring in hot and cold water.  You'd think students would have seen this a million times by their junior year, yet some still were surprised.

This time, many of the story boards were more on target:

  But there were still some interesting interpretations:

Say what?!?

We used the above board (and similar boards in other classes) as a teachable moment about making sure our particles represent what we think is happening, but also make sense based on what we see.  I try really hard not to make groups feel dejected, so I am constantly saying we do this on white boards so we can make silly little mistakes now and erase them easily, instead of making the mistakes on the test.  I had other groups pick out things on this white board that someone might misinterpret-- for example, the hot water particles weren't hovering at the beginning of the demo... or that you can't create matter from nothing...

We then watched the first three Eureka videos on Heat & Temperature.   I found them on YouTube.   After our modeling workshop this summer, I honestly did not anticipate using the Eureka videos.  I hated the idea of showing students something so dated.  But... they do a really good job at making sure there are no gaps in their mental image of particles in solids, liquids, and gases.  I had them answer eight straight forward questions on the videos in their lab notebooks, just to make sure we got some information from them.

So far, this unit seems to be going slowly, but MUCH better than Unit 1!!!