Unit 2 Reflections: Worksheet 3 PVTn Problems

My students... bless their hearts... grr...

Graffiti is beginning to appear on the back of my white boards.  It's mostly your typical, teenage stuff- doodles, smiley faces, although one board had a curse word in marker.  I did not have this problem AT ALL last semester.  I am NOT okay with this.  I'm 99% sure it is happening during our board meetings when they are holding up their boards, and specifically, I'm also 99% sure it's happening in my last class of the day.  In that class, I already catch them trying to hide behind their boards and text, read, sleep...  Instead of addressing the class about the graffiti, I think I'm just going to say from here on out the students need to prop them up at the front of the room.  On a related note, at our workshop, one experienced modeler mentioned that he has hooks hanging from his ceiling to hang the white boards-- if I ever get my own classroom, I'd love to do that.

Anyway- PVTn problems.  I mentioned in my last post, I had zero interest in deploying the "factor" arrow method for solving these problems.  Maybe someday I will change my thinking, but I personally do not see how that is a benefit for them.  Especially not when my students are given the combined gas law on their EOC equation sheet.

I do think the PTVn charts are helpful.  It keeps the students organized, and drawing an arrow for the "effect" helps maintain a connection between their conceptual understanding of particles and the math.

A sample of the PTVn charts on the first page of worksheet 3

I do not think worksheet 3 alone was enough practice and assessment.  In a perfect world, we would have more time to spend on this.  I planned poorly-- I planned for the test tomorrow, thinking we'd complete and check worksheet 3 yesterday.  We didn't check worksheet 3 until today, which cut into out review time.  But we have a 4 day weekend for President's Day/in-service, so delaying the test any longer won't be to our advantage.

Also, I think worksheet 3 is a *bit* overwhelming for low-level standard chemistry students.  There were too many different pressure units right off the bat, including some "minor" conversions.  And by problem #3, they are throwing the STP in there.  I would have liked to have built the students' confidence up with some more straight forward problems before I start switching units or worrying about STP.  If I have such low-performing students next year, I think I will add several easier problems at the beginning.  Also, the problems are boring as all get out.  I'd like to put some "real life" spin on these calculations.

But... after the kid's initial FREAK OUT at having to do some big time algebra with lots of different variables, they didn't seem to have an issue with solving the problems.  I'm curious to see how they handle them on the test tomorrow.

Unit 2 Reflections: PVTn Labs

It's no fail-- my students always surprise me.  Sometimes for the better, sometimes for the worse...

I was having some trepidation about how seriously I should pursue calculating the pressure in a manometer flask like so:

It's not a state standard, so I was going to play it by ear as the students completed Worksheet 2.  If they seemed to understand the concept quickly, I'd have them do those problems.  If not, I wasn't going to fight the battle.  Go figure, they mastered the concept in about 30 seconds.

Overall, they did really well with Worksheet 2.  I would say 85% of the class was even successful at the pressure unit conversions at the end with minimal help from me, and I didn't even tell them it was coming.  Granted a good portion of my students still freeze up like a deer in headlights when they see a conversion, but they can do it with some goading.

We ended yesterday with a Boyles Law lab.  The AMTA lesson plans have students performing 3 labs with Vernier equipment:  P & V, P & n, and P & T.  We don't have Vernier equipment at my school, however I personally have a single LabQuest and probes of my own.  I have mixed feelings about having students do too many Vernier labs, regardless of having the equipment or not.  I feel the students often are intimated by the equipment and software, which causes them to miss the entire point of the lab.  At the same time, I've watched many college students continue to struggle with the Vernier labs.  It would be nice to give my students the exposure now so they're more comfortable with Vernier in college.  I don't think there is a "best" answer when it comes to using Vernier with standard high school chemistry students.

Anyways...

My compromise was for students to do a simple Boyles Law lab using pipets and textbooks that I found on Flinn's website:




Then for Avogadro's and Gay-Lussac's Laws, my plan was to use the Vernier equipment and demonstrate the lab the students were supposed to do from the curriculum.

The Boyles Law lab went pretty well-- it was quick and straight forward.  My first two classes of the day figured out the relationship easily for the most part. Most of their boards looked something like this:

By the end of the day, I found there were more and more student procedural mistakes.  The most common was measuring the length of the water instead of the air, giving them an incorrect graph (this one was doubly incorrect):

I was bummed about their verbal conclusion.  And confused about their particle diagram.

The mathematical expression was really hard for them on this one.  I've found here most students just don't understand inverse relationships.  I showed them the concept of P=1/V, but I'm not sure how many took anything away from the discussion.

The Vernier demos were a huge flop.  The kids were bored to tears.  They didn't understand what I was doing, they just blindly copied the graphs on the screen into their lab notebook.  Seriously, there was zero advantage to pulling out the Vernier equipment for a demonstration in this instance.  I might as well have just talked at them for half the period.

What was most helpful, again, was the PHET simulation.

We also did a KMT reading out of the textbook, or tried to.  I wanted them to read thoroughly and write, but we only had about 10 minutes left at the end of the class to do the activity.  It became more of a "scan for the answer" activity, which I hate.

Tomorrow we will tackle PVTn problems using the combined gas law.  While I plan on using the PVTn charts, I'm not teaching the factor/train-track method they showed us in our modeling workshop.  Not happening.  I'd rather the students be able to plug and chug into the equation that they will receive on the back of their periodic table when they take the EOC.