Weekly Wrap-up: When Life Gives You Lemons, Make an Electrochemical Cell

All too often, we as teachers have grand ideas for projects. So why, despite our best efforts, do they sometimes fall short of our expectations? Perhaps we put too many restrictions on the work and students are left with untapped motivations. Maybe we don’t raise the stakes for the end game and find an audience for students other than their teacher and peers. In hindsight, we probably could have worried less about a standard or objective and more about how the project reflected an actual real-world need or expression of their learning.

But what about the actual process of learning something for the first time? Sure, Tolkien knew that “not all those who wander are lost,” but it’s doubtful that he ever wandered into a Chemistry prep room with bottles labeled in a language as foreign as Elvish to some of us. In school, where teachers are often the “expert,” we’re rarely knee-deep in learning something completely new, and the humbling experience is important to remember when we create projects. Students are going to struggle in places we have a hard time predicting. When you’re learning by doing, if there’s too much too quick or the scaffolding is off, they’ll be wandering further than Frodo did and almost certainly be lost. The journey, though, is worth it when a project is intriguing; so much, in fact, that we as teachers are itching to try.

And that’s why the STEM team has spent a couple weeks trying to charge a battery and cell phone with a solar panel. Since I’m the one who is a novice with electrochemistry, Sarah will check my ongoing quest for understanding in the description of our work below. (Spoiler alert – we haven’t done it yet. Yet.)

The ideal end scenarioelectrode – create a battery that can be recharged from solar panels and that is strong enough to charge a phone. We started with Sarah’s previous knowledge that you can generate a small amount of voltage by basically sending electrons from one metal to another in a setup involing this thing called a salt bridge. Basically, copper sits in a copper solution and zinc sits in a zinc solution. We soaked a strip of paper (our salt bridge) in potassium nitrate and put the ends in both solutions. Then we hooked up a voltmeter and measured 700 milliVolts (mV). Your standard cell phone charger is 5 volts. So make a bunch of these setups and charge your phone, right?

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When the negative electrons move from the iron to the copper through the wire, they interact with the positive ones in the blue copper solution. These become copper solids and you can see it on the copper plate. The exact opposite happens to the iron – when it loses electrons, the imbalanced iron ions essentially “dissolve” into the solution. Hence, corrosion. The salt bridge solution of potassium nitrate, which you see to the left of the copper and the right of the iron, keeps the whole setup balanced. When the blue solution becomes imbalanced from making the copper solid or the iron solution from the corrosion, the positive and negative ions fill the gaps.

Well, wrong. The amount of watts you can get is a product of the voltage and the current.  With this other setup (copper and iron), we again drew significant voltage, but the current was next to nothing. Dana Schlosser helped us measure the resistance (the evil enemy of current) and it was off the charts. A new cell phone charger has a current of 2.1 amps and our setup was meauring about 1 milliamp. There’s a reason batteries are compact – current is also directly proportional to the amount of surface area of the electrodes (copper and iron, in the above example).  So, we increased the surface area with copper and magnesium. Look at the magnesium lose its electrons! (This process didn’t require a salt bridge.)


So, challenges – increase current and find a way to make this process reversable. Well, easier said than done. I looked up NiCd batteries (now illegal heavily regulated, but Sarah won’t let me make one). I looked up NiMh and Li-ion batteries, too, which are used in common electronics. The chemicals are hazardous, which is why my new Chromebook came with a label telling me not to trash the battery.

We took a step back. We both commented that this process is exactly what we want students to go through. So we decided to start small to further our own understanding. Obviously, the next step was to power a bulb with lemons.
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Almost six volts of potential energy from lemons! There is a ton of resistance, but there was enough current generated to light an LED. A small victory for our efforts.

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We still don’t understand why we only pulled 1.7V after hooking up the system or why we got the LED to light with only 0.4mA of current. We’re working on it and Dana has been very helpful.

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Our very first cell. Somehow, lemons light up a bulb and this wouldn’t. Remember – resistance is the enemy of current. Side note – I also lit up a small Christmas light with a solar panel! And I’m wondering if I can charge rechargable batteries with one. But more on that later.

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2 Responses to Weekly Wrap-up: When Life Gives You Lemons, Make an Electrochemical Cell

  1. Mark Hines says:

    As a science teacher, constructivist, and reflective partner I am so happy with this post and what it does to both show your willingness to talk about your learning, your exploration and your adapted to surround failure. Bravo! I love all the work I see you and your team doing.

  2. Pingback: Weekly Wrap-up: Present and Future Innovators at the Riverside STEM Fair | GHS Innovation Lab

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