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Chemistry: Demo: Fruit-Powered Clock


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About this Lesson

  • Type: Video Tutorial
  • Length: 6:45
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 72 MB
  • Posted: 07/14/2009

This lesson is part of the following series:

Chemistry: Full Course (303 lessons, $198.00)
Chemistry: Electrochemistry (12 lessons, $19.80)
Chemistry: Batteries (2 lessons, $2.97)

This lesson was selected from a broader, comprehensive course, Chemistry, taught by Professor Harman, Professor Yee, and Professor Sammakia. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers atoms, molecules and ions, stoichiometry, reactions in aqueous solutions, gases, thermochemistry, Modern Atomic Theory, electron configurations, periodicity, chemical bonding, molecular geometry, bonding theory, oxidation-reduction reactions, condensed phases, solution properties, kinetics, acids and bases, organic reactions, thermodynamics, nuclear chemistry, metals, nonmetals, biochemistry, organic chemistry, and more.

Dean Harman is a professor of chemistry at the University of Virginia, where he has been honored with several teaching awards. He heads Harman Research Group, which specializes in the novel organic transformations made possible by electron-rich metal centers such as Os(II), RE(I), AND W(0). He holds a Ph.D. from Stanford University.

Gordon Yee is an associate professor of chemistry at Virginia Tech in Blacksburg, VA. He received his Ph.D. from Stanford University and completed postdoctoral work at DuPont. A widely published author, Professor Yee studies molecule-based magnetism.

Tarek Sammakia is a Professor of Chemistry at the University of Colorado at Boulder where he teaches organic chemistry to undergraduate and graduate students. He received his Ph.D. from Yale University and carried out postdoctoral research at Harvard University. He has received several national awards for his work in synthetic and mechanistic organic chemistry.

About this Author

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When I was in the fourth grade, I'd go home after school every day and do my math homework in front of the television. And one of the shows that I really enjoyed watching - and to this day, I'll occasionally watch it, when it's on reruns - is Gilligan's Island. Oh, by the way, if you don't know what Gilligan's Island is, it was a show about seven people who get on a tour boat in Hawaii and they're supposed to be going on this short boat ride and there's a storm and they crash and they get stranded on an island. And the makeup of people that get stuck on the island is rather unique. There's the professor - and actually, several years ago, I realized that my goal in life was to be like the professor. But that's another story. There's the rich guy and his wife and then there's the Kansas farm girl and the movie star and the skipper and the first mate, Gilligan.
Anyway, back to the story. Their only connection to civilization is they have this radio. And of course the television show goes on for awhile, and at some point, someone probably said, "You know, those batteries have been lasting a long time." And so they wrote an episode in which the batteries died. And the professor is left to try to figure out what to do. They have no connection now with the rest of civilization because the batteries in the radio are dead.
Well, anyway, the professor notices that the batteries are rechargeable, and rechargeable batteries - the potential can be restored by, essentially, running the batteries backwards - by connecting them to another battery that has an even larger potential to force the rechargeable batteries back to their original state. And in the particular episode, the professor concocts some sort of really weird way of recharging the batteries that involves everybody sitting around the table and there's a coconut with seawater in it and they have to stir it really fast. And I remember this episode, and I remember thinking, "Could that work?"
Anyway, years later, when I was a chemist and I learned a little bit about electrochemistry, I discovered that there is a way to make a battery and it has absolutely nothing to do with stirring seawater, but that you can actually make a battery from a piece of zinc, a piece of copper and then something to serve as the electrolyte. Sometimes this is called a potato clock. Sometimes this is called a fruit-powered clock. And I have an example of one right here. What we have is a half an orange and another half of an orange. And we have a zinc electrode. So here's a zinc electrode and a copper electrode. And these are connected to the leads of a clock - an LCD clock. And then two more electrodes - one zinc and one copper. If this one is zinc, I have to put the copper one on that side. And if this one is copper, I put the zinc on this side. And what happens is these are two batteries where the reaction on one side is zinc going to zinc 2 plus. So it is zinc being oxidized by 2 electrons. And then at the copper, it's not the copper that is being reduced. There's no copper 2 plus or copper 1 plus in the in the orange. So what must be going on at the copper is that the copper is an inert electrode and then something else is being reduced. It could be oxygen in the presence of acid - that's the orange. Or it could be water that could be reduced by the electrons. In any case, something is being reduced.
And the way this is set up - this is a series circuit and it provides just enough voltage to run this little clock. Now it turns out that if you want a large voltage, all you have to do is connect up a bunch of batteries that are of a small voltage in series. For instance, your car battery is 6 lead sulfate, lead oxide, lead cells connected in series. And that's what gets you your 12 volts in your battery of your car to start your car.
Anyway, what I was thinking about was, could the professor on Gilligan's Island have known how to make something like this and would he have had what is necessary to make such a clock? And you'll recall, if you've ever seen the show, that there was an episode in which they suddenly realized they're all getting scurvy. Scurvy is the result of a deficiency of vitamin C. And then Gilligan discovers that there are oranges on the island and so they eat oranges and they get over their scurvy. So they definitely had oranges.
There was also another episode where Gilligan has a cavity and he needs to have the cavity filled, and they accidentally discover some plastic explosives, and the professor doesn't realize that those plastics are explosive, and so he puts plastic into Gilligan's mouth to fill his cavity, and then eventually, Gilligan sneezes and blows the cavities out and explodes one of the huts.
The point is, eventually, what the professor did was, he took the copper from pennies from Mr. Howell and he turned them into fillings for Gilligan. Now, the reality is, you would never make fillings out of copper for reasons that we won't get into here, but they certainly had copper.
And then the question is, what could they have had that would be the other electrode. Chances are, they wouldn't have had zinc lying around, but there is another episode in which a radioactive meteor lands on the island and they have to coat themselves in these radioactive protective suits, and they coat them with lead. And I suspect that, in principle at least, you could make the other electrode out of lead. None of these things are at standard state, so it's not really clear exactly which way the batteries would run, but the point is, they would run in some direction or another. And if you had a whole series of them, in principle, you could create enough voltage in order to recharge the batteries on the radio.
So, the bottom line is, you can write down electrochemical potentials. These are not at standard state, so remember standard reduction potentials are in the standard states. And if you have a battery that's not in the standard state, then you'll have to take that into consideration. But even things that are simple, like zinc and copper and a couple of orange slices, we could use, instead, salt water. The point is that these are just providing the electrolytes. So they could be potatoes, pieces of pineapple. Anything would serve. There's no electrochemistry going on in the orange. It's at the zinc and it's at the copper.
One last thing that might be of interest to you is that pennies that were produced after 1982 are actually zinc just coated with copper, and you can show that by cutting open a penny that was minted after 1982.
If you were ever, then, stranded on a desert island - provided you had oranges and you had new pennies and you had old pennies, you'd have copper and zinc and oranges and so you could recharge the batteries in your radio.
CIA Demonstration: The Fruit-powered Clock Page [2 of 2]

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