Modeling Chemistry Workshop – Day 2 Part 1

After the Mass & Change Lab

Ask your students to draw particles pictures of a solid, a liquid, and a gas.  This could be a quick opener or could just slip in whenever you have 5 minutes or so.  The idea is that we need to establish some standard way that we will draw particle pictures.  This is actually coming long before your students will formally learn about phases, but they will be doing lots of particle pictures, so this is a good point for this discussion.  (Accept that for now some things, like densities, will no be reflected accurately until they are add to “The Story So Far”.)

In our workshop we drew:

  • circles for particles
  • solids with particles touching
  • liquids with particles close but not touching
  • gases with particles spread out
  • the same number of particles when the mass is the same

slg particle pic

This would also be a place where you could introduce physical/chemical change if you wanted.   Thinking back to each part of the Mass & Change Lab:  If you made something new, there was a chemical change.  If you didn’t make something new, it was a physical change.

Unit 1 Worksheet 1 can be completed as homework, although it might be helpful to work on #1 in class together.  Have students whiteboard answers the next day.  Reinforce each of the main concepts from the Mass & Change Lab Discussion.

Logger Pro

Students will probably need a day to learn LoggerPro, figuring out how to enter data and find best fit lines and equations.  You could do this by measuring the circumferences and diameters of various circles.  Or I have had students collect data for the Comparing Volume Units Activity and learn LoggerPro as we enter that.

Comparing Volume Units

As a whole class discussion, ask students what they could measure about a container (a rectangular prism) filled with water and how they can measure it. (These Amac Boxes from the Container Store are cheap and are a great size!)

What Can I Measure? How Can I Measure It?
mass balance (mass the container, then mass the container with water)
how much/quantity/volume 1) length x width x height using a ruler or 2) graduated cylinder

An addition to “The Story So Far”:  Volume is the amount of space something takes up.

The students should write the following in their notes:

Goal: To Graphically and Mathematically Model the Relationship between (at Wheaton Warrenville they call this TGAMMTRB) volume calculated using length x width x height and volume measured using a graduated cylinder

Tools: ruler, graduated cylinder

Depending on how much you want to guide students, you may lead them to a procedure.  Students could pour water into the graduated cylinder and measure volume, then pour into the container and measure height (having previously measures length and width). Each group should repeat the process 6-10 times at different volumes. It might be good to purposefully not mention units (you can bring this up during discussion).  Some students might include the sides of the container in their measurements and some may not – this can also be brought up in discussion as a source of error.  If you use large containers, this activity will take longer and you may want to suggest that students start with a small volume and add to greater volumes by measuring additional water in the graduated cylinder and adding that to the existing volume, rather than measuring the entire greater volume in the graduated cylinder.

Student whiteboards for the activity should include a sketch of their graph and the equation for the line.

Discussion of Comparing Volume Units

Here’s what you need to get out of this discussion:

  • the physical meaning of the slope from the graphs, mL = cm
  • the physical meaning of the y-intercept, no volume in mL = no volume in cm  (empty container) so y-intercept is zero
  • mention labels and titles for graphs
  • briefly touch on best fit lines – should go near as many points as possible
  • mention significant figures (even if you don’t call them that yet) – a need for a standard amount of numbers to report
  • independent variable:  the variable you have control over, the one you choose and manipulate
  • dependent variable: the variable that responds to the change in the independent variable

Make sure all students get this graph in their notes:

mL cm3 graph

Once the graph is labeled, work with students to decide what units are appropriate for the slope.

Since this is a straight line, we can rework y = mx+b with our data to be:

volume (cm3) = 1.00* volume (mL)   {b is zero}

Have students rewrite the slope as a “For every” statement.  “For every 1 mL of water, there is 1 cm3 of water.” or “For every 600 cm3 of water, there are 600 mL of water.”  This is something that Wheaton Warrenville South has been using and it seems to help students really grasp the mathematical relationships.  Students will often try to use “per” but often don’t really understand it, so this is a great substitute.

Next Up:  Mass and Volume, Glugs in Modeling Chemistry Workshop – Day 2 Part 2