What am I doing to help kids achieve?
How do I know when they are there?
What is the evidence?
I have been teaching for more than 20 years. Everyone I meet who is not a teacher assumes that during the summer teachers kick back, sit by the pool and drink Margaritas. I try to explain that one of my favorite activities is to get to work on ideas that I can never do during the school year. One of my biggest struggles with students is to try to explain what happens when items, specific inorganic salts, dissolve in water. It might sound simple to me and you. Research shows that students have many real misconceptions when it comes to explaining inorganic salts dissolving in water. My own experience along with other teachers I know is that we are amazed and sometimes frustrated with trying to help students understand the simple process of dissolving, especially with ions. A key piece of equipment is a good conductivity tester. Just got done making a stack of them and can't wait to have students try them. But back to "dissolving"....
Here are a few ideas that might help students. First, there is the idea of trying to have students explain and understand the dissolving process on the particulate level, the macroscale and the symbolic. Second, Bob Worley introduced me to the idea of "puddle chemistry". To put it simply, students place a small drop of distilled water on an acetate sheet. They then place different crystals on opposite sides of the drop or "puddle". The really cool part is that if students were to use a crystal of sodium carbonate on one side and copper (II) sulfate on the other then they will eventually see a small line form in the middle of the puddle which is the insoluble solid copper (II) carbonate. This method has the ability to be so much more powerful than mixing the two solutions together and observing a solid form. If students do not understand the dissolving process then they certainly will not understand dissolved compounds in two liquids forming an insoluble solid. The "puddle" chemistry method forces students to develop some explanation about a solid dissolving and then forming a different solid. The only part that could make it better is using a conductivity tester throughout the different stages. Students could check the conductivity of distilled water, then distilled water with a small amount of an ionic solid dissolved. The idea of "ions" would hopefully help them develop the idea of dissociation. The only way to explain the conductivity part would be if there are ions present. I tried this and it failed miserably. I just did not have a good conductivity tester. I tried ot make one but it was giving false positives. I found plans for a new one that I believe is much better than ones I have tried in the past and has many advantages.
David Katz and Courtney Willis have written a paper that also includes a DIY conductivity tester and a lab. Here is what I love about their idea for the conductivity tester. All of the pieces are easily available. I made some minor modifications. First, I went to the hobby store and bought graphite rods that are used in building remote controlled airplanes. They conduct, are strong and unreactive. I am using these as my electrodes. Thanks Bob Worley for this idea. The other modification is the power source. Nine volt batteries are expensive. I was able to get a box of 12 volt DC power sources from a cable/cell phone store for free. The people at the store often have to swap out old modems with new modems and they trash the old stuff. The power sources work great for this type of application. I will never have to worry about buying a 9 V battery again. Here is the great part about the conductivity tester...there are two LED lights. One is green and the other is red. They are both hooked up to resistors but the green one is hooked up to a resistor with slightly higher resistance than the red one. If there is a solution that conducts really well, both lights are on. As the conductivity drops, the green light dims and only the red light will go on. It shows different AMOUNTS of conductivity. Now it is close to becoming not just a qualitative tool but also a quantitave tool. If this were not enough, there are also plans for a conductivity tester with a buzzer. So...in theory...this could be used with dissolving. Students could be asked to explain what would make the different lights go on and what is happening in the water during the stages.
Totally off topic...BCCE 2016 is right around the corner. I hope to be at the ChemEd Xchange booth Tuesday morning. Stop by and say hello. If you cannot make it, follow me on Twitter at @ChadHusting.