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  1. #11
    Ian Grant's Avatar
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    Why not make it up properly like Kodak themselves suggested with 7.5gms Borax and 1.5gms Sodium Hydroxide instead of 10gms Kodalk/Sodium Metaborate ?

    Ian

  2. #12
    BradS's Avatar
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    I had this same question some years ago....I'm not a chemistry person so, it took me several hours to figure this out but, here's the way I see it....

    2NaOH + Na2B4o7(10H2O) + 5H2O <-->> 4NaBO2(4H2O)

    2 mols lye + 1 mol Borax (in water) is equivalent to 4 mols Kodalk in water

    80g lye + 381.37g Borax (in water) is equivalent to 551.42g Kodalk in water.

    divide each of these by 5.5142 and we have:

    14.5g Sodium Hydroxide (Lye) + 69.2g Borax dissolved in water is equivalet to 100g of Kodalk (dissolved in water.


    Of course, you may wish to divide by 55.142 to get...

    1.45G Lye + 6.9g Borax (dissolved in water) is the equivalent of 10g of Kodalk dissolved in water.


    The difficulty with this whole approach is always measuring out the Lye accurately. It suck water out of the air so fast you can actually watch it gain weight on a scale.

    (EDIT: or, do as Ian suggests above!)

  3. #13
    Ian Grant's Avatar
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    Quote Originally Posted by BradS View Post

    (EDIT: or, do as Ian suggests above!)
    More importantly as KODAK SUGGEST

    Ian

  4. #14
    Rudeofus's Avatar
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    As mentioned in that other thread, there is a nice procedure described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax. I'd add half the moles of Na2CO3 as there are moles of NaOH in the original recipe and go from there.
    Trying to be the best of whatever I am, even if what I am is no good.

  5. #15

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    Quote Originally Posted by Relayer View Post
    But now I want find other solution for buffer with same pH, because I don't like working with NaOH.
    This statement by the OP seems to be forgotten. He already knows how to make sodium metaborate from borax and sodium hydroxide but would like an alternate.

    BTW, you cannot make sodium metaborate from sodium carbonate and sodium borate from just mixing them in solution. The only way to make it is to fuse the two chemicals at red heat. The average person does not have the equipment to do this.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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  6. #16

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    Quote Originally Posted by Rudeofus View Post
    As mentioned in that other thread, there is a nice procedure described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax. I'd add half the moles of Na2CO3 as there are moles of NaOH in the original recipe and go from there.
    hmm...

    Na2B4O7.10*H2O + 2*NaOH + 5*H2O --> 4*NaBO2 + 16*H2O

    so

    Na2B4O7.10H2O + Na2CO3 + 6*H2O --> 4*NaBO2 + 16*H2O + CO2

    381.37g of Borax + 106g of Sodium Carbonate = 551.2g Kodalk (sodium metaborate + water NaBO2·4H2O )
    and for 10g of Kodalk we need mix 6.92g of Borax with 1.92 of Sodium carbonate

  7. #17
    Rudeofus's Avatar
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    Quote Originally Posted by Gerald C Koch View Post
    BTW, you cannot make sodium metaborate from sodium carbonate and sodium borate from just mixing them in solution. The only way to make it is to fuse the two chemicals at red heat. The average person does not have the equipment to do this.
    And doesn't need to. Relayer doesn't want to supply the world market with 99.9% pure Kodalk, he wants a buffer at pH 8.2 for a photographic developer. At this pH any extra CO32-, HCO3- or CO2 won't make much of a difference. If it did, the dev could not be used after much exposure to air anyway.

    Mike Wilde gave his recipe specifically because NaOH picks up CO2 after some time. I really don't think there is much of a difference between making it with carbonate vs. lye but I'm open to learning.

    @Relayer: If you are concerned about the surplus of CO2, you could leave it standing in air for a while. I'm not aware of any harm air could do to metaborate.
    Trying to be the best of whatever I am, even if what I am is no good.

  8. #18

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    Quote Originally Posted by Rudeofus View Post
    And doesn't need to. Relayer doesn't want to supply the world market with 99.9% pure Kodalk, he wants a buffer at pH 8.2 for a photographic developer.
    yes, you right. I'm find some easy-to-mix buffer solution that give me different range of pH and and also allow substitute kodalk

    just make some experiment: in 1l of water at 32C dissolve 1.92g of Sodium carbonate. then add 6.92g of borax - its dissolved very quickly! solution is muddy, but clear after 2-3min. check pH - 9.2 at 24C. now put this solution in open bottle and will be recheck pH later
    Last edited by Relayer; 07-20-2012 at 05:14 PM. Click to view previous post history.

  9. #19

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    Quote Originally Posted by Rudeofus View Post
    As mentioned in that other thread, there is a nice procedure described by Mike Wilde how to make Kodalk from NaOH and Borax. I am quite confident this procedure can be easily modified to make Kodalk from Na2CO3 and Borax.
    Certainly one can make a buffer from carbonate and borate but the last sentence is not true. Sodium carbonate is not sufficiently alkaline to react with borax in water like sodium hydroxide can.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  10. #20

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    Quote Originally Posted by Gerald C Koch View Post
    Sodium carbonate is not sufficiently alkaline to react with borax in water like sodium hydroxide can.
    not agree - you forget about hydrolyze.

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