Sodium Bisulfite > Sodium Metabisulfite

Discussion in 'B&W: Film, Paper, Chemistry' started by Bruce Osgood, Nov 7, 2006.

  1. Bruce Osgood

    Bruce Osgood Membership Council Council

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    I'm mixing a formula that contains 5g sodium bisulfite as a buffer to hydroquione. I don't have bisulfite but I do have metabisulfite. Is this apples and oranges or is there a conversion?
     
  2. Lowell Huff

    Lowell Huff Inactive

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    They are the same thing.
     
  3. juan

    juan Subscriber

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    I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
    juan
     
  4. Bruce Osgood

    Bruce Osgood Membership Council Council

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    Thanks Juan,
    I'll go with 1 to 1 until I hear otherwise. Thank you,
     
  5. Robert Hall

    Robert Hall Subscriber

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    They are not the same and the ph is different. I would ask Gerald Koch about this.
     
  6. Ryuji

    Ryuji Member

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    Why do you say that? When dissolved in water, metabisulfite forms bisulfite ion and they are the same thing. In amateur darkroom formulae I doubt anyone ever used pure sodium bisulfite in dry form as an ingredient; it's a misnomer.
     
  7. Ole

    Ole Moderator Staff Member Moderator

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    In solution, they're identical.

    There's a difference in the crystal structure, but that doesn't matter at all as soon as it's dissolved.
     
  8. Robert Hall

    Robert Hall Subscriber

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    Thank you for the clarification. It was my understanding that Metabisulfite had a lower ph, is this not true?

    thx
     
  9. Gerald Koch

    Gerald Koch Member

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    When Kodak sold chemicals a mixture of sodium bisulfite and sodium metabisulfite was sold as sodium bisulfite. If you look at the MSDS for sodium bisulfite it is listed as 58 - 99% sodium bisulfite and 0 - 42% sodium metabisulfite. Pure sodium bisulfite is sold as a 40 - 45% solution rather than as a solid.

    Kodak recommended using the same amount regardless of which chemical the formula mentioned.
     
  10. Bruce Osgood

    Bruce Osgood Membership Council Council

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    Works for me. Thanks to all who contributed.
     
  11. dancqu

    dancqu Member

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    There is no metabisulfite in solution. None we be
    brewing. At crystallization two bisulfites join loosing
    a molecule of water; so the meta. In solution the meta
    joins with water; so two bisufites. The meta is more
    concentrated by one molecule of water.

    Likely there is a source for one and/or the other.
    The ph in solution is that of the bisulfite. Dan
     
  12. Ryuji

    Ryuji Member

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    Not that it matters a lot in terms of darkroom mixology, but this is simply untrue. In concentrated solution of sodium bisulfite, metabisulfite is present.
     
  13. dancqu

    dancqu Member

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    "None we be brewing" I did qualify my statement.
    Besides you and I know better. Concentrated
    solution or not, as a species metabisulfite
    will exist at ten to the minus who knows
    how many zeros. Dan