In trying to pack and hour or more of material into a half hour or less,
a few key ideas and methods of authentic assessment were omitted.
I mentioned that you can have your students use square mm, cm and dm
cutouts, and cubic cm and dm (plastic, paper or cut-down milk cartons)
to demonstrate the concentrations of each dilution in two-dimensional
and three-dimensional space, respectively.
An advantage of having the students prepare their own 1m square grid is
that they can be used for extension activities that demonstrate
understanding. For example, working individually or in teams (on the
same or on different activities) you might have them:
1. Create a multi color population graphic (2-D or 3-D) using subsets,
e.g. start in one corner of the grid and color in enough mm squares to
represent the # of students in the class, switch colors and continue to
fill in enough to represent the # of students in the school, then add
population of the city and county. Finally ask what they would have to
do to add the population of their state and of the U.S. (Older students
could use cut-off milk cartons 10 cm on a side to build a 3-D model)
2. Have the students prepare a 2-D model of the composition of the
atmosphere, e.g. the bottom 79% being N, approx. 20.9% for O2 then
include the trace amounts of C02 (@ 3 ppb), water vapor (will vary),
stratospheric ozone, etc. This provides a powerful visual for
discussion of how important greenhouse gases are, even though the
concentrations are extremely small.
3. Obtain a copy of your local water quality report and have students
represent the actual quantities of major contaminants in their water
supply and/or the EPA's figures for MCLs (maximum contaminant levels).
For oceanography, have students create models of the composition of
seawater. These activities bring home the differences of various
substance's concentrations, some in ppt (parts per thousand), others in
ppm and ppb.