Calling all amateur soap chemists -- Disodium EDTA experiment

Discussion in 'Lye-Based Soap Forum' started by DeeAnna, Jan 10, 2019 at 8:30 PM.

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  1. Jan 10, 2019 at 8:30 PM #1

    DeeAnna

    DeeAnna

    DeeAnna

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    Short version:
    Would people who have Disodium EDTA (I really do mean Disodium, not Tetrasodium!) do me a favor -- would you please try to dissolve Di EDTA in the lye solution you use for your next soap batch and report back? Some questions I have for you --
    Does the Di EDTA dissolve easily in your lye solution?
    If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
    Do you have any observations, comments, tips, or tricks about using Di EDTA?
    ***

    Long version:
    Suppliers of soap and cosmetic ingredients may sell two forms of the chelator EDTA -- there's Disodium EDTA and there's Tetrasodium EDTA.

    Tetra EDTA is highly soluble in plain water, so it's easy to use for many hand crafted bath and beauty products such as soap, lotions, etc. Di EDTA, on the other hand, is not nearly as soluble in plain water.

    For this reason, many of us who use EDTA prefer to buy the Tetra version. Unfortunately, it's easy to forget there are two versions and purchase Di EDTA by mistake. In a recent thread, we discussed if and how Di EDTA can be successfully used if that's the version a person happens to have. See https://www.soapmakingforum.com/threads/how-to-make-tetraedta-in-39-solution.72729/

    The key to dissolving Di EDTA is to dissolve it in a high pH (alkaline) solution, not plain water. So that got me to thinking -- any lye solution that would be used to make soap will have a much higher pH than is strictly needed to easily dissolve Di EDTA. So why not add Di EDTA powder to the lye solution and then make soap as normal?

    Problem is -- I don't have any Di EDTA to test this theory, which is the reason for this thread. Carolyn (@cmzaha) says it works for her to dissolve Di EDTA in the lye solution she plans to use for soap making. She reports it just dissolves without any trouble.

    Would others who have Di EDTA do me a favor -- would you please give this a try and report back?
    Does the Di EDTA dissolve easily in your lye solution?
    If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
    Do you have any observations, comments, tips, or tricks about using Di EDTA?​

    More info:
    What is a chelator: https://classicbells.com/soap/chelator.html
    Using tetrasodium EDTA in soap: https://classicbells.com/soap/EDTA.html
    Using disodium EDTA in soap: Use the same dosage by weight as Tetra EDTA. (See link in the line right above.) You can use KOH or NaOH solution for dissolving Di EDTA.​
     
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  2. Jan 10, 2019 at 10:29 PM #2

    Misschief

    Misschief

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    I'm at work right now so can't really concentrate. Will answer tonight. I did try it on the weekend.
     
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  3. Jan 11, 2019 at 2:01 AM #3

    Misschief

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    Ok, I'm home now. I went with what Salted Fig wrote in one of her posts in the How to Make TetraEDTA thread. Towards the end of her post, she finished with:

    Conclusion:
    It's probably worth adding the extra hydroxide if you are using Disodium EDTA, but not entirely necessary.

    Original Tetrasodium EDTA: 1000g of oil, 5g of Tetrasodium EDTA
    Disodium version with NaOH: 1000g of oil, 5g of Disodium EDTA and 1g additional NaOH
    Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.5g additional KOH
    Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.6g additional 90% KOH


    The batch of soap I made used 1000 g of oil, which is what most of my batches are, so I added 5 g of Disodium EDTA and 1 g additional NaOH. The DiEDTA was added to my lye solution. It dissolved fairly readily but did cloud the lye solution enough that I felt I should strain it into my oil mixture. There was no residue left in the strainer, which was my finest strainer. It did take a little extra stirring to incorporate the DiEDTA; I even used my mini blender, being very careful to make sure nothing splattered. I wasn't sure whether I should add the powder directly to the dry lye or into the water before adding the lye. I ended up adding it after the lye was dissolved.

    I used a 33% lye solution but did add 1g extra lye.
     
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  4. Jan 11, 2019 at 2:25 AM #4

    DeeAnna

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    I would add Di EDTA powder to the lye solution.

    If you add Di EDTA to just the water before adding the NaOH (or KOH), the Di EDTA is not going to dissolve well. It's all but insoluble in plain water.

    I was wondering if a more concentrated lye solution might cloud when Di EDTA is added. I know Tetra EDTA will precipitate out of NaOH solutions when the lye concentration is about 35% or higher. The lye solution will look like milk and may even thicken up. If the lye concentration is below about 35%, this problem doesn't happen. It stands to reason that Di EDTA would probably do likewise.

    Thank you, @Misschief!
     
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  5. Jan 13, 2019 at 2:24 PM #5

    kayak1987

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    Disodium EDTA is just an intermediate form between EDTA and Tetrasodium EDTA
    the switch between the varoius form of EDTA is an equilibrium driven by the concentrations of sodium and hydronium ions (pH) and regulated by the constants of acidity and solubility.

    Considering this, is "easy" to predict that in a solution with NaOH (where NaOH is in excess respect to "EDTA") so at High pH:
    -EDTA will be very soluble beacuse the H+ are pulled out by the OH- and in solution you have EDTA(4-) now with his equilibrium with the various 1,2,3,4Na forms
    -DiNaEDTA will be still soluble but more influenced by the common Na Ion
    -Tetra Na EDTA didn't get any advantage of the pH and to dissolve needs to loose at least 1 Na+ that is in competition with the Na+ released by the NaOH

    Other things to consider are that if there are other Ions in the solution you have new equilibriums to consider, dissociations and chelations equilibria
    so if you don't use good deionized water is very hard to predict what is that gives to solution the milky look.

    Antother thing to consider is that Saponification is a stechometric reaction where you need all the lye Sodium to turn the acid to soap, as well as EDTA is competing for sodium when can't no more stay in solution (because of water get consumed by saponification and after, evaporating during cure time), so if you are using EDTA or Di EDTA is better to consider not to discount too much the Lye or to add some Table salt to prevent side reactions that can lead to release fatty acids (and maybe rancidity problems)
     
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  6. Jan 13, 2019 at 7:31 PM #6

    DeeAnna

    DeeAnna

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    In this thread, I'm specifically asking soapers to share how-to-do-it (or how not do it) tips for using disodium EDTA in everyday soap making.

    Science has its place, but empirical, practical knowledge is what I'm after here. Thanks....
     
  7. Jan 15, 2019 at 11:26 PM #7

    glendam

    glendam

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    I could try in my next batch, however, I am a bit concerned since I do not know much about how they actually work, only that tetrasodium EDTA is for soap and disodium EDTA is for lotions because of the ph (I have both and make both soaps and lotions). By adding disodium to the the lye water, is it becoming tetrasodium?
     
  8. Jan 16, 2019 at 1:18 AM #8

    DeeAnna

    DeeAnna

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    Yes, that's correct. Tetrasodium EDTA is very soluble and disodium EDTA is only slightly soluble in plain water. As you increase the pH by adding NaOH or other alkali, the disodium form gradually converts to the tetrasodium form. (I'm simplifying a bit here, but that's the essence of what happens.) We discussed this in this thread: https://www.soapmakingforum.com/threads/how-to-make-tetraedta-in-39-solution.72729/

    I don't want anyone to do this experiment unless you are really curious about the outcome and want to try it for yourself. If you are fairly new to making soap or are uncomfortable with the idea of a failed batch of soap or of making a mess, I recommend that you do not participate in this experiment. Let the crazy folks like me give it a go and figure out what works first.
     
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  9. Jan 16, 2019 at 2:54 AM #9

    glendam

    glendam

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    Thanks for explaining. I love experiments, just got Kevin Dunn’s book. I usually take videos of my soapmaking too, so I will report back once I get to make soap again, hopefully this week. I’ve been making for over a year. :)

     

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