Sulphite & Metabisulphite questions on heat

Discussion in 'B&W: Film, Paper, Chemistry' started by Athiril, Oct 25, 2010.

  1. Athiril

    Athiril Subscriber

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    It seems I am having trouble mxing up sulphite from metabisulphite.

    (I can only buy sodium sulphite here and from pool shops not from the photo chemical suppliers who only have metabisulphite.. and I want the potassium salt, edit: Vanbar has sodium sulphite now)

    I am following:
    K2SO5 + 2KOH = 2K2SO3 + H2O

    When I mix it I usually get undissolved matter remaining, requiring filtration, is this because of the heat produced from the reaction by the KOH?

    What is the best method of production? Metabisulphite in water, KOH in water, add KOH solution to metabisulphite? Add metabisulphite solution to KOH?

    Metabisulphite powder to KOH solution? KOH flakes to metabisulphite solution?



    I also remember reading somewhere that heat will 'wreck' the sulphite, so am not able to boil off the remaining water to collect dry sulphite?
     
  2. clayne

    clayne Member

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    Tangent... I remember the days when we used to have chemistry kits as kids. Anyone else remember those? Nowadays you'll never see anything remotely like that, not after McVey and not after 9/11.

    Granted, as a kid (during my pyro era) I would mix all of the chemicals together just for fun.
     
  3. Gerald C Koch

    Gerald C Koch Member

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    Dissolve the metabisulfite in water then add the KOH solid gradually with stirring so as not to generate too much heat.

    Adding KOH solution or solid to solid metabisulite could produce a lot of steam causing the mixture to splatter.

    Use safety goggles or a face shield when working with strong bases or acids to prevent eye damage.
     
  4. michaelbsc

    michaelbsc Member

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    Yes, but McVeigh's method was so simple any farm boy who's ever seen a fertilizer fire could reproduce it.

    What are we going to do? Go back to fertilizing with fish heads and manure? The country would starve.
     
  5. clayne

    clayne Member

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    Yeah well my point was that due to past occurrences it's now more difficult to get basic chemicals.
     
  6. michaelbsc

    michaelbsc Member

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    I see. You are right about that.
     
  7. Athiril

    Athiril Subscriber

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    I haven't had splatter issues at all, but yes a lot of heat, so I was wondering if the heat affects the sulphite.
     
  8. Gerald C Koch

    Gerald C Koch Member

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    No, you cannot get past 100 C while there is water present. To decompose the sulfite you would have to get much hotter than this.
     
  9. Athiril

    Athiril Subscriber

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    Im sure Ive done it slowly and kept temps down and had no undissolved matter... guess I will try again, perhaps I will try drying it out to powder too :smile: