Analytical Chemistry and LED Colorimeter

LED Colorimeter

"What are we doing to help kids achieve?"

A colleague of mine suggested that it would be great if somehow we could fit something in about analytical chemistry. I really like the idea, but I am just not sure how to fit it in. Students always assume chemistry is just all about just working with chemicals. The idea that they could build their own instruments might inspire some students in ways that previously may not have been possible. Is there a way students could do chemistry, build their own instruments and get a taste of analytical chemistry?

I was inspired by Tom Kuntzleman's blog, (and corresponding Journal of Chemical Education (JCE) article), on using a smartphone as an absorption spectrometer. I tried it out and it worked well. I continued to look for something that I could have the students build, was low cost and somewhat microscale. I found a JCE article, A Simple, Small-Scale Lego Colorimeter with a Light-Emitting Diode (LED) Used as Detector, that was helpful. The authors made a Lego colorimeter with LED lights. Various prototypes worked extremely well. I was trying to find something a bit simpler. Legos can get expensive. I think I might be on the correct track with film canisters.  

    Here is what I did. First I bought some red LED lights. Next, I hooked the LED lights up to an 390 Ohm resistor. I taped together two 1.5 volt AA batteries to get a 3 volt battery and tested the light. If you have never worked with LED lights before it should be noted that the current can only go one way. If at first you test the light and it does not work, simply switch the poles of the battery and try again. I needed something inexpensive to use as a cuvette holder. Our photography teacher gave me a bag full of black plastic film canisters.  Inexpensive plastic cuvettes fit perfectly in a film cannister. I glued one to the cap. I took a 1.5 inch metal screw and heated it over a candle. This allowed me to poke a hole straight through the film cannister. I placed my LED light in one hole. In the other hole I placed a second LED light. This second light I hooked up to a volt meter and set the dial to "millivolts". The film cannister is a great container that blocks out extra light. I did a quick test to make sure my LED light worked and that I was getting some "millivolts" from my detector. LED lights are fascinating. Not only do they provide different colors of light due to "band gaps" in different metals, they also act as a mini solar panel (see my previous blog entry).

   I was ready to test. First I used distilled water and then tested .1M, .2M and .35M copper (II ) nitrate solutions. After finding the percent transmittance and absorbance and graphing with concentration, I got a .95 r2 value.  Not great, but not bad for a colorimeter that costs about $2. So the question will this work with students? Not sure but I am getting ready to take the plunge. I will report back. Do you have a lab that involves students building their own instruments in a unique way? Please let me know...I would love to hear from you.