Sulphuric acid substitute

Discussion in 'B&W: Film, Paper, Chemistry' started by Alessandro Serrao, Nov 15, 2004.

  1. Alessandro Serrao

    Alessandro Serrao Member

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    I'm a newbie on this forum so please don't shoot my back... :smile:
    I've got the following question: is there a substitute for sulphuric acid in the b&w reversal process, and if yes, what quantity or concentration?
    Thanks in advance.
     
  2. Dr.Kollig

    Dr.Kollig Member

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    The reversal step needs quite a strong acid, most recipes I remember are 10-15 ml of sulfuric acid, of course if you are more comfortable you can use diluted sulfuric acid in a higher amount.
    I could not find the source but I think you might be able replace it with either the sodium hydrogen sulfate or potassium hydrogen sulfate, roughly three times the weight. Maybe it was Maco or Foma reversal formula.

    To be honest I would recommend to use the acid and just be careful, battery acid is sulfuric acid.

    Regards,

    Wolfram
     
  3. wdemere

    wdemere Member

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  4. Jordan

    Jordan Member

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    Yup -- Sodium bisulfate, also known as sodium hydrogen sulfate (do not confuse with sodium bisulfite) dissolves readily in water to produce a very acidic solution equivalent to dissolving both sodium sulfate and sulfuric acid in water.

    I've been using "pH Minus" pool additive, which is at least 95% sodium bisulfate (the balance being probably sodium sulfate) for a home reversal process and it seems to work fine. I am having a bit of a problem with over-bleaching, though.

    E-mail me if you need more details.
     
  5. Alessandro Serrao

    Alessandro Serrao Member

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    Can I use potassium alum sulphate in substitution of sulphuric acid?
    Can I use the alum as a hardener as well?
     
  6. Adrian Twiss

    Adrian Twiss Member

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    Slightly off thread but I cannot get Sulphuric Acid in concentrations of greater than 10%. Whilst I am happy to use 10x the amount when a formula calls for concentrated Sulphuric Acid is Sodium Bisulphate a universal replacement for Sulphuric Acid?
     
  7. Jordan

    Jordan Member

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    Potassium aluminum sulfate solutions are probably weakly acidic but not nearly enough to acidify a bleach. The reason why sodium bisulfate (sodium hydrogen sulfate) can replace sulfuric acid is because it is an 'acid salt' of sulfuric acid -- sulfuric acid partially neutralized with base, as it were. When sodium bisulfate is dissolved in water, it forms a solution that is identical in composition to one produced by dissolving both sulfuric acid and sodium sulfate in solution in equal concentrations.

    I wouldn't want to experiment with mixing alum with a bleach. The results could be very unpredictable or dangerous.
     
  8. Jordan

    Jordan Member

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    It can replace it in many formulas. As I mentioned in the previous post, when you dissolve sodium bisulfate in water it creates a solution equivalent to one created when equimolar amounts of sulfuric acid and sodium sulfate are present. If this sodium sulfate doesn't interfere in your application, you should be fine.

    Any more questions, just let me know.
     
  9. Jordan

    Jordan Member

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    Actually, the more I think about it, the more I realise that what I wrote above is not strictly true -- that the sodium bisulfate solution is equivalent in action to an equimolar mixture of sodium sulfate and sulfuric acid. It is probably equivalent to something other than a 1:1 mixture. In any case, the sodium bisulfate can successfully be used to acidify a bleach and for some other photographic purposes.
     
  10. Ole

    Ole Moderator Staff Member

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    Jordan, you were right the first time: One mol of sodium sulfate plus one mol of sulfuric acid = 2 mol of sodium bisulfate. If I knew how to make subscripts in this system I'd write it out properly.

    This mixture will never get the pH as low as "real" sulfuric acid will, but it might be enough.

    And by the way: "Bisulfate" means a salt of a metal, hydrogen and sulfate, like NaHSO4. Sulfate has no acid hydrogen, like Na2SO4. Sulfuric acid is H2SO4.

    Sulfates without hydrogen are alkaline, and can not be used as a substitute for an acid. But sometimes what you want is the sulfate ions, sometimes the acidity. If it's sulfate you're after, any sulfate will do. If it's acidity, acetic acid will do.

    So it really depends on the application.
     
  11. Ole

    Ole Moderator Staff Member

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    And while I'm at it - I myself would never under any circumstances use concentrated sulfuric acid if I could get by with a 10% solution. Concentrated sulfuric acid is a truly horribly nasty stuff! The only acid I fear more (and have used) is hydrofluoric.
     
  12. Alessandro Serrao

    Alessandro Serrao Member

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    ...and about bichromates

    :sad: It seems that here in Italy, where I live, I cannot get access to potassium permanganate, because of local laws that forbid the selling.
    So I've searched around and found a substitute for it: potassium bichromate.
    Probably one of the nastiest stuff out there: http://chemdat.merck.de/pls/pi03/we...een=110&cid=983541252&pg=1&s=7778-50-9&lang=4
    is carcinogenic, mutagenic by inhalation, it's classified T+ and has a R-phase 49-46 (the nastiest).
    So I'm at a loss: what I'm gonna do?
     
  13. Ole

    Ole Moderator Staff Member

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    Alessandro, is that bichromate or dichromate?

    Potassium dichromate (K2Cr2O7) is used in many bleaches, while I've never heard of a use for Potassium dichromate (KHCrO4)!

    Anyway: The DIchromate is nasty, oxidizing, possibly carcinogenic, and quite safe if handled carefully - just don't throw it around. Potassium permanganate is all of the above, in addition it's strongly oxidizing, explosive when mixed with some other chemicals, stains everything, etc...

    If you can get K2Cr2O7 but not K2MnO4, there's probably a reason for it: Dichromate is safer!
     
  14. Alessandro Serrao

    Alessandro Serrao Member

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    Potassium dichromate is the same as potassium bichromate: they are merely synonym, as you can see from the Merck web page.

    And potassium permanganate is way less toxic that the bichromate counterpart (is not carcinogenic nor mutagenic for example), again refer to http://chemdat.merck.de/pls/pi03/we...869389&pg=1&s=potassium%20permanganate&lang=4
     
  15. gainer

    gainer Subscriber

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    You might try Edwal Tray Cleaner. It will bleach silver images to a form that is soluble in sulfite solution without dissolving the undeveloped silver halide. It has been a long time since I tried it, so can't remember a particular dilution, but that part of the process goes to completion anyway, so it shouldn't matter too much. In any case, try it on something less than precious.
     
  16. Alessandro Serrao

    Alessandro Serrao Member

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    Thanks Patrick but Edwal is not accessible in Italy. I think I'll stick with the Foma b&w slide kit, available at 19€ per 8 rolls. Too nasty the bleaches are to me :wink: . Thanks anyway.
     
  17. Ole

    Ole Moderator Staff Member

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    Ehrm .... In this case, I disagree. Di- is not Bi- , in this case; in almost all others they're equivalent. I make an exception for Chromium and Silicon.

    If Merck claim that Permanganate is not carcinogenic or mutagenic they're ignoring 30 years of evidence to the contrary.
     
  18. Ian Grant

    Ian Grant Subscriber

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    go to B&Q, (UK market) they have a drain cleaner which is concentrated Sulphuric Acid.

    It did clean my drains !

    Or buy from Scientific & Chemical Supplies in Wolverhampton but you need to order on company headed notepaper.
     
  19. Alessandro Serrao

    Alessandro Serrao Member

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    Well, all msds sheets on the net state that KMnO4 is not carcinogenic nor mutagenic: if you have other evidences I'm very interested, so please post them here.
    I miss your explanation of bi- not being di-: could you be more precise?
     
  20. Jordan

    Jordan Member

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    Bi- vs. di- first. The use of 'bisulfate', 'bicarbonate' and names like them is not considered 'proper' chemical form nowadays because of this very ambiguity. Those names have a lot of historical precedent behind them, though, which is why we use them. They come from simple stoichiometry -- think of it this way -- sodium bisulfate (NaHSO4) has twice the number of sulfate ions per sodium ion that sodium sulfate has (Na2SO4). This is where the 'bi' comes from. The 'di' notation would refer to the relative 'numbers' of each ion.

    It is likely that in other languages 'bi' and 'di' are used interchangeably or 'bi' is used where 'di' would be used in English. I know this to be the case in French. This may be where Alessandro and Ole's disagreement stems from. I have never heard of 'acid chromate' salts as there is a dichromate-chromate equilibrium that is pH-dependent.

    To complicate matters even further, there is an additional nomenclature that uses 'acid salt' terminology. NaHSO4 would then be called 'sodium acid sulfate'. So NaHSO4 = sodium bisulfate = sodium hydrogen sulfate = sodium acid sulfate. Confused yet?

    There are specific reasons why bleaches are acidified with sulfuric acid (or sources of it like sodium hydrogen sulfate). The acid required has to be strong enough to generate the oxidizing species ('permanganic acid' in the case of permanganate bleaches and chromic acid in chromium bleaches) and I doubt highly that acetic acid is up to the job -- it is simply too weak an acid (in terms of acidity constants). The acid must provide an anion that forms a soluble salt with silver, which sulfuric acid does (silver sulfate is water- soluble), so that the oxidized silver dissolves into solution rather than remaining in the film. Finally, the acid must itself not have a detrimental effect on the remaining silver halide in the film. Sulfuric acid seems to fit the bill nicely for all these requirements. I've never seen a reversal bleach that is not acidified with sulfuric acid or one of its derivatives (I would be very interested in hearing of any examples that are).

    Ole, you are right about my posts. I was right the first time. I agree with you that sulfates without hydrogen form alkaline solutions, but this effect is very weak, as the 'second' proton in sulfuric acid is still pretty strong (though not as strong as the 'first'). People bathe in magnesium sulfate solutions as a muscle relaxant (Epsom salts).

    Re: toxicity -- there was a vigorous debate about this a few months ago in another thread which I will not re-hash. Suffice it to say that I am very surprised that dichromate is available for sale in Italy while permanganate is not for toxicity reasons. Dichromate is a potent carcinogen and persistent, while permanganate tends to decompose pretty quickly and is not nearly as toxic (it is used in dermatological preparations). AFAIK Kodak replaced the dichromate in their TMX reversal kit with permanganate for that very reason.