Unit 3: Energy and Moving Particles (duration: ~2 weeks, or 8 class meetings)

Since the first bit of the traditional “Unit 2” was covered in the previous unit, this unit starts with pressure. Otherwise, there was no real modifications to the normal sequence.

Unit 4: Describing Substances (duration: ~2-3 weeks, or 10-12 class meetings)

We started this unit with a lab activity: Comparing Water and Ethanol. Students used some concepts and skills from previous units to compare two substances that look pretty similar. In the modeling materials, much of this is done in discussion/demo. But as my students needed to work on lab skills, it made sense to make this a mini-lab activity. Some major additions:

• Introduces “vapor pressure” as a way to measure how easily a substance evaporates. Since we’d just used the pressure sensors, it was pretty easy for them to collect data.
• Students investigate the pure substances as well as mixtures of the substances (50/50 and 70/30).

At the end of the activity, students compared data with their tablemates, then we compared results as a whole class. There was some variation from group to group on the values for vapor pressure (mainly due to the quality of the individual pressure sensors) but all groups observed that the vapor pressure for ethanol was nearly twice that of water.

Students then went on to complete the post-lab activity with their lab partners. In addition to particle diagrams, students make a connection between vapor pressure and rate of evaporation. There’s room also for them to predict what might make some substance evaporate faster than others. We had some great discussions about this, and it helped also to understand why heats of vaporization and fusion differ for different substances. Students do look up information thermodynamic data for the substances (Fun fact: Siri searches Wolfram Alpha for this info). Next, they sketch heating curves for ethanol and water, then make predictions about how they could separate the two.

The next day, we go over the post-lab activity. Then, I ask them to sketch what a heating curve would look like for a 50/50 mixture of ethanol and water.  Then, using a LabQuest 2 and a distillation set up, we collected the data.

After this, we go through the iron/sulfur/iron-sulfur/iron sulfide sequence from the modeling materials. Then the rest of the unit proceeds in the normal sequence.

I like the changes in this unit — it is great to have students make the connections to unit 2 and 3. It was also great to be able to revisit their predictions when we study intermolecular forces in more detail later in the course.

Unit 2: Energy and States of Matter (Duration: ~ 3 weeks, or 13 class meetings)

This unit began relatively normally, with diffusion demos and storyboards. We watched the Eureka! videos, and we discussed measuring temperature, and how to represent cold and hot particles in motion. We had a great discussion on our particle representations, when forced to remove all words from our whiteboards.

After a discussion of thermal expansion of liquids and solids, rather than moving on to pressure and gases, we went right to heat and temperature. Continuing with the Icy Hot Lab, we introduced energy bar charts to describe the changes qualitatively.

For time reasons, we did not complete the Lauric acid activity, but one valuable addition was a worksheet for students to practice drawing temperature-time graphs for substances other than water. We finished with quantitative calculations for phase and temperature changes.

This change in sequence seemed natural. I will definitely repeat next year.

I’m currently in my 8th year of teaching, 7th year of teaching Chemistry, and 5th year as a modeler. It is not an exaggeration to say that my experience with modeling has changed my entire teaching philosophy, and the way that I relate with students. It has also had an impact on how I teach chemistry not only at the introductory level, but also in my AP-level courses.

Starting this year at a new school, with no other modelers in the department, I planned to depart from the modeling framework. After about a week and a half of getting to know the kids and where they were, I quickly reverted back to my old ways. I’ve made some modifications, additions and omissions, that have worked well so far, and will probably continue to use moving forward.

Here’s an overview of my first unit.

Unit 1: Chemical Foundations (Duration: ~3 weeks, or 13 class meetings)

Introductory Activity: #chemchat

This activity had a few goals:

• Give the students an opportunity to talk about what they did this summer (which they are always dying to do on day one).
• Get to know something new about their classmates (and for me, to get to know them).
• To see what they already know (pre-assessment).

The students have almost all come from physics the year before, some conceptual, and some computational, so there was a wide range of background in science skills and practices. So each station was devoted to a specific skill or content knowledge.

• graphing
• lab equipment
• making observations, forming a hypothesis
• making measurements and metric conversions
• dimensional analysis
• prefixes and suffixes
• chemical and physical properties
• lab safety

This was a successful activity, but I don’t think I will need to use it again.

Lab Safety

I usually show clips from Flinn’s “Starting with Safety video,” but this year had students watch this video for homework, and list as many safety violations as they could find. On average, each class found around 24. From this, we organized the violations into groups (personal protection, handling chemicals, and common sense). We added to the list as needed, and took a safety tour through the lab space.

Baggie Lab

Water + baking soda + calcium chloride + phenol red = lots of observations. After one trial, we compared our observations as a class. Then, we sought to determine which substances were responsible for which of the changes we observed. Each lab table “dropped” one of the substances, and recorded new observations. We then made a HUGE data table on the front board. where each group reported out which changes they observed in their trials. Using the shared data table, students answered the following questions in pairs:

1. Which ingredient is responsible for the rise in temperature? Explain.
2. Which ingredient is responsible for the drop in temperature? Explain.
3. Which ingredient is responsible for the color changes? Explain.
4. Which ingredients are required to produce all of the changes observed in the initial baggie?
5. Summarize the four signs of a chemical reaction, and cite 1 trial (besides the initial) where that sign was observable.

While the main goal of this was to give students experience with collaboration and analyzing data, it is continuing to pay off in later units.

Making Measurements

This lesson wasn’t too different from the “reading scales” lessons in the modeling chemistry unit, but since the students had already learned significant figures in physics, my emphasis was on uncertainty in measurements. We did a quick lab activity where we practiced this skill. Students then completed the “Reading Scales” modeling worksheet for homework.

The next day, we did another measurement activity. We did a similar activity when I was a TA for a general chemistry lab back in the day. The goal here is to investigate precision and accuracy of the tools that we use. The following day, we shared average percent deviations for each scenario, and had a good discussion about precision and good lab practices. It also gave us clear data for using a graduated cylinder over a beaker for measuring volume.

This has “stuck” with most of my students (at least so far), so it was definitely a worthwhile activity.

Mass and Volume (and the rest)

It’s around this time that I made the gradual switch back to the modeling curriculum. While we didn’t go back to do the mass and change activity, we began to incorporate particle-level representations here. I didn’t do as much emphasis on graphical analysis, in terms of y-intercept and correlation, since we were graphing by hand at this point. Using relative densities of solids, liquids and gases, were able to build a sufficient model to move forward.

Next year, I definitely hope to include the mass and change activity. Fortunately, students have exposure to both significant figures and dimensional analysis from freshman physics, so I am happy to continue to use that time saved for building measurement skills and good lab practices.

Next up: Energy.