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What do the blue and pink color of the rust indicator shown mean?

  1. Oct 12, 2014 #1
    Hello, everyone.
    What do the blue and pink color the rust indicator shown mean?

    Let say, the mixture of potassium hexacyanoferrate(III) and phenolphthalein is the rust indicator. And we use to detect the rusting of an iron nail. And the result is: the tip, head region of the nail appear blue color; the straight region appears pink color.
    Is that the blue region shows Fe2+ ions formed? And, the pink shows hydrogen ions present?

    But, even it shows these ions are present, what does it mean? The blue area is rusting? And the pink area no rusting?

    Confused :( please help!!
     
  2. jcsd
  3. Oct 12, 2014 #2

    Borek

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    Staff: Mentor

    Yes.

    No, quite the opposite - it shows where the amount of H+ is small.

    Where do they come from?
     
  4. Oct 12, 2014 #3
    Thanks for replying.
    Sorry, my bad. That is a typo.
    I should write 'hydroxide ions' ,
    the pink area shows the presence of HYDROXIDE ions .
    But, i dont get it, even hydroxide ions is produced, what does it mean? Does it mean the pink area part is rusting?
     
    Last edited: Oct 12, 2014
  5. Oct 12, 2014 #4

    Borek

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    Staff: Mentor

    No, it contains possible rusting product.
     
  6. Oct 12, 2014 #5
    Thanks again.
    So simply speaking, the blue area means the rusting has already taken place/ the rust is formed . And the pink area means it is going to form rust (coz hydroxide ions are produced before rust is formed.)
    Am i right? :)
     
  7. Oct 12, 2014 #6

    Borek

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    Staff: Mentor

    I think both ions are produced at the same time, they just show where different half reactions occur (they don't have to go in teh same place, as long as there is conductor present).
     
  8. Oct 13, 2014 #7
    Thank you
     
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