Kool-Aid Concentration & Particle Modeling

One of the toughest things about chemistry is that you can’t see those stinkin’ little particles that make up everything.  How I envy the physics teachers whose students can calculate the velocity of a car zooming down the street in front of our school and the biology teachers whose students can dissect the kitty cat.  In other science classes, students can view things under a microscope, observe the effect of gravity on an object, and compare the colors of minerals.  But in chemistry, we’ve got those darn particles that you can’t see.  And the behavior of those particles help a chemist understand so much about matter and its properties.

It’s always been important to me to help students “see” particles.  In my 20-plus years of teaching I’ve used magnetic “atoms” on my blackboard to help kids visualize elements, compounds, and mixtures.  I utilized these same magnetic atoms to emphasize the Conservation of Matter when we balanced equations.  My students have used mini white-boards to predict how changes in temperature and volume affect the pressure exerted by particles of gases.  Any now that I teach in a 1:1 classroom with iPads, it’s easy to get students to draw particles of all colors and sizes .

Kool-Aid solutions A, B, and C

There’s one more little thing pushing me to draw particles:  NGSS Science and Engineering Practices.  In SEP-2 the Framework identifies “Developing and using models” as an essential skill that students must learn.  Models can be incorporated in a variety of ways, but I find drawing particle pictures to be particularly effective in helping students understand relationships between variables.

Students react to dilute Kool-Aid

I recently adapted a Kool-Aid Concentration lab in my Solutions Unit.  In the past this lab was an easy-breezy introduction to molarity and solution making.  I decided to add some modeling ooomph to the lab by challenging students to draw the particles of solute and solvent found in varying concentrations of solutions.  I also incorporated an awesome PhET simulation that allows students to adjust the amount of solute and solvent in a solution and measure the molarity of the resulting solution.  Note to iPad users:  There’s an HMTL 5 version of this simulation.  So excited!!!

Here are some improvements that I found in student learning:  

• I heard students discussing the “ratio of solute to solution” for the first time in 20 years.
• Students improved their conceptual understanding of the meaning of molarity. (“The water’s got more stuff dissolved in it!!)
• They made the connection between the number of dissolved particles and the color of the solution.

If you’re interested in modeling with particles, give this Kool-Aid Concentration lab a try:

Students sampling their Kool-Aid solutions

Kool-Aid Concentration Lab