Modeling Chemistry Workshop – Day 3 Part 1

Unit 1 Worksheet 3

This worksheet really makes students think about density from so many different angles.  They are looking at and interpreting particle pictures and mass vs. volume graphs, and even using lab generated data.  This is not a worksheet that you want students to do alone though, as I think the discussion that it generates as they think is really helpful.  If you are pressed for time, at least have them start in class.  (Have a medium amount of time for this?  Maybe have them do #1, #4 and #7 in class.)  Then assign the rest for homework.  In all cases, whiteboard it!

What do we want to get out of Unit 1 Worksheet 3?

  • How do we show density with particle pictures (what does more/less dense look like?)
  • Using a graph
  • Density = slope for a mass vs volume graph, more dense = steeper slope
  • “For every” statements can help push students away from the common misconception that heavy = dense and towards seeing that density is a conversion factor

Density of a Gas Lab

In this lab, we capture CO2 from Alka-Seltzer mixed with water by connecting tubing from the test tube where the reaction occurs to a container filled with water and displacing the water.  Most groups seemed to get a density that was about 10 times bigger than it should have been, but still MUCH smaller than densities they will have seen for liquids and solids.  (I’m not thrilled with these results and may see what can be done to improve them later this year, but for now…)

What do we want to get out of the Density of a Gas Lab?

  • Densities of gases are MUCH smaller than those of liquids and solids – and particle pictures should reflect that
  • Reinforce significant figures
  • Reinforce for every statements

After a whiteboard discussion of the Density of a Gas Lab, have students draw particle pictures for solid aluminum (2.7 g/mL), liquid water (1.0 g/mL), and CO2 gas (either use lab data or substitute with the actual value of 0.0020 g/mL).  (Make sure to give them the densities.)

Pictures should look something like:

density slg

The idea is for students to understand that particles in gases are much more spread out than those in solids or liquids.  (Notice that rather than draw 1000 particles and 2700 particles, I just did “x 100”.)  For now these pictures assume that all particles are the same size (we’ll revisit that assumption later).

Unit 1 Worksheet 4

This worksheet is fairly straight forward.  Students are practicing using a mass vs. volume graph to determine density, mass and volume given different information and in different ways.  There is a quiz in the Modeling Chemistry materials that goes along with this worksheet.

Unit 1 Worksheet 5

This is a worksheet based one the website http://www.vendian.org/howbig/. You would need to have access to computers with internet for this one (at least one for every lab group).  This activity helps establish how small atoms are.  It may be a good one for a day when you need a sub and it seems to be okay fitting in whenever in the year.  (In other words, if you skip it now and come back to it, that would be okay.)

Unit 1 Worksheet 6

This worksheet is labeled as a dimensional analysis worksheet and has students practice with conversion factors.  At Wheaton Warrenville South, they have sometimes instead had students find a conversion factor, create a graph showing the conversion factor, and write a “For every” statement.  I’ve done the worksheet, but I like the idea of getting students extra practice with graphing and what a conversion factor really is.  I may do a combination of both this year.

Unit 1 Test

This brings us to the end of Unit 1.  The Modeling Chemistry materials include a review and test for the unit.  You will likely need to modify them for your own classes.

In our training, we discussed how to approach the tests.  Some schools allow students to use binders as a “toolbox” on tests.  If you go this route, you may want to keep a strict limit on time (since some will not study and be flipping through binders during the whole test).  You could also have binder check questions like: “Write the answer to # ___ on worksheet __ ” (Remember to change the question # or worksheet if you have multiple sections.)

Lab Practical for Unit 1

The Thickness of a Thin Layer – This lab comes from the Modeling Chemistry materials.  Students measure length, width, and mass of regular and heavy-duty aluminum foil rectangles and use the density to find volume, then thickness.   If you’ve done Unit 1 Worksheet 5, this has a tie-in to emphasize the smallness of atoms.

Another option would be to find the density of unknown solid metals. Students could be ask to graph the densities, identify which would float/sink, draw particle pictures, and write “for every” statements.

Modeling Modalities

I should maybe have included this earlier, since it was first mentioned in the welcome presentation on the first day.  But it can kind of fit in wherever because I feel like it is something to come back to throughout the year and to make sure you are connecting to, especially in your assessments.

Overall learning objectives for students:

  • I can explain in words
  • I can make and interpret a graph
  • I can draw a particle picture
  • I can use a mathematical model
  • I can apply the model in the lab

I feel that the first unit is excellent at incorporating each of these.  Some later units may not hit every area, but they come close.  This may be another thing for me to tweak in the future…

Up Next: Smelly particles, particle movement demos, pressure

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