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Experiment and pu tiron nail into water

  1. May 22, 2010 #1
    So i did an experiment and pu tiron nail into water and serveral days later it starts to rust.

    and i looked at the book and the chemical process is
    1)Fe loses electron
    2) that electron + oxygen + water produces hydroxide
    3) hydroxide and Fe ion reacts and form Fe(OH)2, green rust
    4) green rust + oxygen become red rust + water

    but i dunno why it is red rust that is formed on the nail. If the pH level is low will it becomes red rust or stays at green rust?

    THX!
     
  2. jcsd
  3. May 23, 2010 #2

    Astronuc

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    Staff: Mentor

    Re: rusting

    Crystal structure of green rust formed by corrosion of cast iron
    http://www.nature.com/nature/journal/v259/n5540/abs/259200a0.html

    http://en.wikipedia.org/wiki/Iron(II)_hydroxide
    Look at the possible reactions of Fe and aqueous solutions, and also at the forms of Fe oxides, hydroxides and oxyhydroxides.

    Are there any cation impurities or alloying elements?
     
  4. May 25, 2010 #3
    Re: rusting

    well the h2o will have impurities, and the nail is actually steel and iron?

    As part of the experiment i am also to de rust the nail.

    would the nail suppose the gain weigh after electrolysis? Because when the nail rust it gains weigh, and if de rust will it lose weigh? but my nail gains weigh after electrolysis and I have no idea why is that...
     
  5. May 25, 2010 #4

    Astronuc

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    Re: rusting

    The nail is probably steel, i.e. an alloy of iron. It would gain mass from the oxidation of the steel components, i.e., pickup oxygen in the form of oxides, or hydroxides.
     
  6. May 26, 2010 #5
    Re: rusting

    well yes when the nail form rust it is heavier but im not sure about the cathode (rusted iron) will gain or lose weight. I re-tested again at school day and still got the same result. So my question is how come the nail rust it gains weight, and when the nail being de-rusted it gains weight again?

    Oh.. also the anode iron (sacrifical iron) forms green stuff aorund it, im not sure what that is too!
     
    Last edited: May 26, 2010
  7. May 26, 2010 #6

    Astronuc

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    Re: rusting

    How much mass is gained?

    In addition to forming oxides with iron and other steel components, there may be spinels or other complex oxides. Is the electrolyte solution aerated or de-aerated water?

    Note: reduction occurs at the cathode. So mass deposition would occur at that cathode.

    http://bouman.chem.georgetown.edu/S02/lect25/lect25.htm
    bouman.chem.georgetown.edu/S02/lect25/e3a.jpg

    Also note the different reactions with water. Even in electrolysis, if one liberates hydrogen, the oxygen is available to react with the cathode.

    What reactions are taking place in the cell, particularly at the cathode?
     
  8. May 27, 2010 #7
    Re: rusting

    the cathode nail takes 25mins to gain 2.36 -> 2.4. This is not too accurate becuase there are those (green stuff?) form around the nail and when i pull the nail out and measure the weight those green stuff fall out and stay in solution.

    solution is HCl

    the rust on cathode nail should be forming FeCl2 then will form iron as the cathode nail becomes negative? Is hydrogen gas also produced at cathode?
     
  9. May 27, 2010 #8

    Astronuc

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    Re: rusting

    By 2.36 -> 2.4, is this a mass changing from 2.36 g to 2.4 g? I presume units are grams.

    Does one measure the nail both times in the same condition, i.e. dry?
     
  10. Jun 1, 2010 #9
    Re: rusting

    sorry my computer was having some problems...

    yes it changes from 2.36 to 2.6 in grams and are both measured in the same condition
     
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