## Thursday, April 18, 2013

### Defining Terms: Mixture, Dissolve, and Solution

The boys had to define some terms before we continued with our study of rocks and minerals.  We wanted to understand the difference between rocks and minerals and in order to do that we needed to understand what a "mixture" was.  Also, our study of minerals is going to quickly take us to a study of crystals.  In order to make our own crystals we had to learn what a "solution" was.  This work also led us to the concept of "dissolve."

We started by picking up a few demonstrations from Building Foundations of Scientific Understanding (BFSU).  First we visited Lesson A-7 to pick up part one, "Defining a Mixture."  I used some common examples such as the mixture of red and white class beads above.

Another easy example is a handful of loose change.

I wanted to be sure that they understood that mixtures are not always made of only solids so, We reflected back on the day that I let them mix together all the liquids in the refrigerator (but didn't repeat the experience!).

Next, we jumped to lesson A-9 "Dissolving, Solutions, and Crystallization."  The first part is called "Some Things Dissolve:  Solutions and Mixtures."  There are a lot of activities to choose from here.  The boys started by making a drink for themselves with a beverage powder (we used Crystal Light).  We usually avoid that type of thing, but in this case the coloring allowed the boys to see what happened to the particles as they fell through the water.  There were wavy trails of color.  Particles got smaller and some disappeared as they sank in the water.

The boys learned that when something has apparently disappeared into water we say that it has "dissolved."  We reflected on what we had already learned about particles and determined (with the help of the script in BFSU) that the particles of color and sugar are actually clumps of particles and that the clumps had come apart into particles too small to been seen.  We could see it in this instance due to the coloring.  Also, as you can see above, the boys enjoyed their beverage along with trail mix which I pulled out as an example of a MIXTURE.

To show the boys an example of particles dissolving so that they cannot be seen, we repeated this same experiment with plain white sugar and water.  The boys learned that "solutions" are a special class of "mixtures" in which one or more of the ingredients are dissolved in the liquid.

We also mixed a teaspoon of flour into a glass of water.  The water was cloudy rather than clear.  Flour-in-water remains a mixture.  It is not a solution.

BSFU suggested using a bottle of soda to demonstrate that the ingredients in solution may be gases.  Under pressure the carbon dioxide remains dissolved.  When the pressure is released we can see the packages of air particles, or bubbles, as we did in our particles demonstrations the other day.

We ended by making several solutions of dissolved table salt in water.  This led into the beginning of our crystals work.  Our new understanding of mixtures led us directly into some rock versus mineral work as well.  However, you'll have to wait for my next posts!