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Formic Acid Question

Discussion in 'Tanning' started by Pirate, Feb 21, 2010.

  1. I thought someone out there that knew a little more about how chemicals react could explain this to me. When I first mix up a batch of pickle I use about 1oz per gallon to get a 1.5-2 mix. The put the salt and stuff in too. When I'm ready to put hides in, I spin them in a washer and then wrap them in a towel for about 15 minutes to get them as dry as possible. I do that hoping not to change my mix to much when I put them in. As always the next day the pH rises because of the hides I put in. Now my question, why does it take more formic to get the pH back to 1.5-2 than it did to originally make the batch.
     
  2. cyclone

    cyclone Posts: 400001

    The little bit of water on a cape when first placed into the pickle is not going to affect pH much unless your water is very basic. The following post deals with what you are asking about. Pay particular attention to the "Ionic Strength"..


    http://www.taxidermy.net/forum/index.php/topic,15866.0.html

     

  3. TD

    TD My GGG Grandfather John "Tanner John" King b 1820

    Cyclone...............You might want to re write that in Layman terms ??? ;)
     
  4. JE

    JE Well-Known Member

    So, does this mean that the more hides there are in the pickle, the more acid ( formic ) will be needed to maintain PH levels ??
    and also that the more "fatty" the hides are, then even more acid is needed ?? or am I just in too deep !!!!!!! LOL
     
  5. cyclone

    cyclone Posts: 400001

    Yes on the more hides, not sure where you are getting the "fatty" thought from..

    That is layman's terms where I work...
     
  6. JE

    JE Well-Known Member

    1 hydrogen ion will also react with 1 active unit on protein or fat or collagen. Once it does it is used up and no longer adds to the pH of a solution....so the pH rises.

    It was this sentence that I was getting the "fatty" thought from, like I said, in way to deep LOL
     
  7. cyclone

    cyclone Posts: 400001

    Acid does not react quickly with fats, the point made meaning that for every acidic ion used up there is a resultant rise in the pH of a solution.

    There are more sites for the acidic protons to react with when a hide in freshly introduced. The pH rises. Let's say you add another ounce per gallon to bring it back down. You started out with X ounces of acid. You added X ounces to get it back down to the desired level.

    Theoretically therefore, a solution with 2X ounces of acid in the beginning shouldn't experience a rise in pH.
    The solution with 2X ounces has twice the ionic strength as the 1X pickle.

    Why not add that extra acid up front?
     
  8. joeym

    joeym Jeannette & Joey @ Dunn's Falls

    Cyclone, I think you gave a good explanation.
     
  9. Ok that makes sense to me and I understand. Now my question would be is it be better to make an entire new batch of acid for the second day, or use the same batch and add the extra acid.
     
  10. joeym

    joeym Jeannette & Joey @ Dunn's Falls

    Normally, if you make a batch to fit the item being tanned, no additional modifications need to be made...ie..9 oz citric acid, 3 lbs salt per 3 gallons of water for a wt deer cape. The effects of osmosis on the saline and neutralizing some of the acid have already been factored into this formula.
     
  11. cyclone

    cyclone Posts: 400001

    Use the same batch just add more acid.

    To answer your original question: ( Wanted to make sure I had it correct)

    The answer being:

    Once you have used up that acidic proton you are left with an equivalent amount of formate ion. Formate ion will attract hydrogen ions from the solution and you now have a buffered solution. Buffered solutions resist changes in pH. Adding more formic acid will indeed lower the pH but only after those formate ions' hunger for acidic protons is satisfied.

    Scientists indicate an acidic proton by the symbol H+, a positive ion. Negative ions, such as formate are denoted with a negative superscript. For simplicity's sake (formate)-.

    With the formic acid molecule you have:

    ( H+)(formate-)

    In a pickle they are separated kind of like:
    ( H+) + (formate-)

    Once that hydrogen ion is used up by the hide the formate ion will pull a hydrogen ion from the nearest source which is either a free hydrogen ion or a water molecule itself. Pull the hydrogen ion from a water molecule and you are left with:

    ( H+)(OH-) ______> (OH-)

    (OH-) is your base and causes a rise in pH.

    Got all that? Test in the morning...
     
  12. joeym

    joeym Jeannette & Joey @ Dunn's Falls

    Damn cyclone...I've had plenty of chemistry...bbbbut, I don't wanna have to take your test...I know I'd Flag it!!!
     
  13. cyclone

    cyclone Posts: 400001

    It's been simplified, the real equations can be a bear.... ;)
     
  14. bill@hogheaven

    [email protected] New Member

    8,015
    3
    I wish I had a better understanding of chemistry than I do.
     
  15. joeym

    joeym Jeannette & Joey @ Dunn's Falls

    Bill:

    Chemistry is the course that made many a potential doctor change his/her major to data processing when I was in school. It was the most dreaded course for freshmen on a college campus...besides calculus and physics. Somehow, I muddled my way through it.
     
  16. pittmjj

    pittmjj 150 okie public land 8pt

    66
    0
    Its all a plus (+) minus(-) game
    (+)=acidic
    (-)=Basic

    Hide=organic compounds

    Organic compounds= (-) charge on ionic "surface" (generally)

    Acid=H+ "donator"

    (- )from hide attracts + from acid...like magnets

    + from acid gets pulled out of solution

    subsequently the ratio of (+) to (-) in solution moves in favor of (-) and pH goes up

    Salt typically also creates an environment for pH to easily increase to a point associated with the pH of that salt. The more "NA+CL- "(salt) you put in the more free (-) you have floating around, and although "NA" does have a (+), it is a very large ion, and doesnt stick well to (-) surfaces...kinda like the difference btw using 1 nail to secure a 3 in piece of 2x4 to a wall in the case of H+, and using that same 1 nail to secure an entire 4x8 sheet of plywood in the case of NA+....1 (+) , 1 nail. Thats also why you can disolve so much salt into a relatively small amount of water (weak ionic bond). But salt added to the solution in large quantities provides the function of a buffer. This buffer makes it harder to change the pH in either direction so once you get it adjusted, it wont spike or fall rapidly, but still allows for H+ interaction with the hide due to the plywood/ 2x4 scenario.

    so you pretty much have a system that lends itself toward a basic pH, and the idea is to exhaust all the possible ionic exchange sites with a solution of free floating (+) that (+) being an H+ ion from the added acid. This "displaces" (in quotes cause its not just Nitrogen or Hydrogen alone) the nitrogen in nitrogenous compounds to an extent where those tissues are rendered for all practical purposes undigestable, or at least not palitable to bacteria.....but that doesnt seem to detour dogs.
     
  17. cyclone

    cyclone Posts: 400001

    You did fairly well right up to the point you made with the salt, NaCl. It in no way shape or form influences pH. Pure NaCl has never and will never add or subtract to the buffering capacity of a solution. While it does influence the ionic strength of a solution it has no influence on the acidity or basicity of a solution.
     
  18. Rhino

    Rhino Too many irons in the fire will put the fire out!

    Thanks Cyclone! A good read. ;D
     
  19. pittmjj

    pittmjj 150 okie public land 8pt

    66
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    Your right cyclone, NACL doesnt directly affect the relative pH in a solution. Thats why I said "Salt typically also creates an environment for pH to easily increase to a point associated with the pH of that salt". NACL has a dis-association constant that allows it to easily go into solution due to its week ionic bond strength. During the time I spent working in various environmental labs, and throughout my time in school working towards an applied env. chem degree (s), I learned the buffering capacity of "salty" solutions for extractants, as they tend to be stable due to the concentration of "free" ions (both cat- and an- ions), but the solution tends to as you would expect adopt or trend toward the pH associated with the ion having the lowest charge density for that salt...in this case Cl-. Case in point hypo-chlorite (bleach) or the clorine tabs for the pool, make your hands slippery...its basic, lots of Cl-. Cl- and H+ trend toward one another and tend to bind at a pretty strong level. As I am writing this I realize I have neglected to illistrate the true characteristics of a solution in that there is never really "stability", just a sort of chaotic bouncing back and forth between this ionic combo and that one and then the next or the other and back until some amount of stronger bonds are created. This is to say that a constant reaction, or interaction is taking place until "all" reaction sites, or exchange sites have been exhausted and a large % of the free ions "used up". Subsequently NACL doesnt directly raise the pH, but after a bit, in a salt saturated solution an environment is created which allows for trending toward the pH of the anion in that salt, providing that solution is water based. You are in the case of tanning sacrificing a small amount of pH lowering capacity of your acid to stabilize the solution with salt. Incidentally, and for an illustration, sodic, or natric soils which contain high levels of both Na+ and Cl- have a certain criteria for classification as sodic or natric. Part of that requirement is, simply put, a basic pH. This also holds true for surface water, or consumable water sources. Cyclone, Im not saying any of the previous statements you made are wrong at all, the only reason I posted was to attempt to add to the body of knowlege you had already shared, and maybe communicate it in a way some who initially didnt understand could.
     
  20. pittmjj

    pittmjj 150 okie public land 8pt

    66
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    You seem to know your stuff cyc. what line of busines you in? I understand the general machanics of what is going on in the tanning system, but i have found that using the exact same mixture for generally the same sized specimen i dont always get the same results. My additions (ingredients) are the same and subsequently i am creating the a consistant solution, so my controlable variables are fixed, other variables being only the composition of the water i use, and some range in temp, what could be influencing? The hide i am dealing with is the only answer i can come up with...your thoughts?