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Solution of silver ions turning amber

  1. Aug 11, 2010 #1
    I've been making solutions of silver ions by hooking 20-30V up to 2 silver electrodes in distilled water and noticed something interesting. The solution starts off as clear and by adding a bit of NaCl, AgCl precipitates out so theres definitely Ag+ ions in there. If I leave the solution for a few days it turns amber coloured. This is the colour
    IMAG0177.jpg
    whats going on here? I haven't bothered to retest for Ag+ ions but the only theory I've come up with is that the Ag+ ions have been reduced somehow and neutral Ag atoms absorb some light.
     
  2. jcsd
  3. Aug 11, 2010 #2
    Hmm, I'm not sure, but it's likely that it is related to the formation of silver oxides. Add some base and see if the color deepens.
     
  4. Aug 12, 2010 #3
    Photochemical reduction of the AgCl back to nanoparticles of silver, maybe?
     
  5. Aug 12, 2010 #4
    Acut: I added NaOH but no color change at all.

    minerva: Solutions with no AgCl turn amber.

    Oxidation to Ag2O is the best theory so far IMO. I did read that silver nano particles absorb some wavelengths of light and the result is an amber color though so I wonder if the cations could be getting reduced somehow. Does that kinda thing occur? Spontaneous reduction of cations. Enough theorizing though I'll just add some NaCl and look for AgCl precipitate.
     
  6. Aug 12, 2010 #5
    Hm, I think it's not Ag2O.
    Addition of strong base to Ag+ solutions produces silver hydroxide, which, in turn, reacts with oxygen from the air to form the oxide. So addition of silver hydroxide would either deepen the collor or produce more of this amber-collored compound.

    I'm not a silver expert, however.
     
  7. Aug 12, 2010 #6

    Borek

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    Try to write reaction equation.
     
  8. Aug 12, 2010 #7
    I'd guess this,

    2Ag(OH) + O2 -> Ag2O + 2OH-

    But I've only read its description, never saw its chemical equation.
     
  9. Aug 12, 2010 #8

    chemisttree

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    So you are electrolyzing in distilled water, eh? Not very efficient, at least at first. It is likely that CO2 is being absorbed into the solution and you are making small amounts of silver carbonate.
    At 20 to 30 V you are certainly hydrolyzing water as well so your solution and your silver electrodes have oxygen present as well as the reducing hydrogen gas. Hydrogen gas can react with silver to produce silver hydride which can be a variety of colors from red to black.
     
  10. Aug 13, 2010 #9

    Borek

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    Check if it can be balanced.
     
  11. Aug 14, 2010 #10
    @Borek: Hm, I never realized that!

    But I'm sure I read about this reaction.

    It's amazing how much I learn with your posts!
     
  12. Aug 14, 2010 #11

    Borek

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    In short - Ag+ was already oxidized, it doesn't change its oxidation state, so it doesn't need oxidizer.

    --
     
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