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Homework Help: Soda Clocks?

  1. Apr 25, 2010 #1
    1. The problem statement, all variables and given/known data
    My teacher used soda to power up a clock. He used a magnesium and copper wire, and soda (sierra mist)

    I have to explain why and how this happened.

    2. Relevant equations


    3. The attempt at a solution

    My teacher said it had something to do with oxidation-reduction. I think it has something to do with the carbonic acid or phosphoric acid found in most sodas. I found an explanation for a similar experiment which uses a potato, but I can't quite understand it.

    "The potato contains phosphoric acid. This acid causes chemical reactions to occur at each of the electrodes (galvanized nail and copper penny). The reaction at the copper electrode strips electrons from the copper and attaches them to the Hydrogen ions (2H+) in the phosphoric acid. This depletes the electrons on the copper electrode which makes it "hungry" for more. The process creates Hydrogen gas.

    The galvanized nail provides the Zinc needed for the other reaction. The phosphoric acid dissolves the Zinc in the nail and liberates electrons from the Zinc atoms. The liberated electrons stay on the electrode and the resulting Zinc ions (Zn++) migrate into the acidic juices of the potato. This results in an excess of electrons on the Zinc electrode. If a wire is connected between the Zinc nail and the copper penny, electrons will flow. This flow of electrons is the electrical current that makes the digital clock function."
  2. jcsd
  3. Apr 26, 2010 #2
    What your teacher constructed is a basic battery.

    This is how it works (simplified):

    The two different metal wires act as electrodes. The solution enables them to exchange ions. One wire will decay and another will gain ions. This creates voltage which enables a current to flow through the clock, making it work.

    For a more detailed explanation, read on Electrochemistry. You should have a section on electrochemistry in your general chemistry manual.
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