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Citric acid as a chelator

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coffeetime

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I live in an area with very hard water, and I wondered if it is advisable to use a little citric acid in with the KOH? Would that act as a chelator for hard water?
I searched the liquid soap board but the only references I found were for using CA to neutralize.
I did look up potassium citrate, as I assume that is what would be formed (?) and it doesn't indicate chelation at all, just alkalinizing, so I am probably completely off base. :-? Is there any way to reduce soap scum with liquid soap?
 

The Efficacious Gentleman

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I think it does, but I am not sure.

If in doubt, could you whip up a batch of sodium citrate using the baking powder method (or using NaOH if you want) and add in some Sodium Citrate rather than citric acid?
 

DeeAnna

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You can add citric acid to form citrate as a hard water chelator. In a KOH soap you'd be making potassium citrate, but that's not the point really. It's the citrate ion that is the chelator, not the sodium citrate or potassium citrate molecule.

The liquid soapers don't discuss this because their mindset is not focused on that aspect of what citrate can do. They are only looking at citric acid as a neutralization agent for excess lye, as you noted. But when they do neutralize with citric acid, they are inadvertently also making citrate -- they just don't know it.

If you use citric acid in the sense of its being a chelator and not a neutralizer, then add the extra lye needed for the citric acid to react with --
10 g citric acid neutralizes 6.24 g NaOH.
10 g citric acid neutralizes 8.42 g KOH.

ETA: Wikipedia has a little bit about citrate's ability to chelate (bind up) metal ions such as calcium to prevent blood clotting and to descale boilers. These applications aren't about soap, I agree, but the principle is the same. https://en.wikipedia.org/wiki/Trisodium_citrate
 
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coffeetime

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Thank you so much, DeeAnna! That is exactly the info I was hoping someone would have. That's awesome. I'm hoping to make myself a test shampoo and I think the citrate would help with the horrible buildup I get with bar soap (which I haven't tried adding citric acid to yet). So many projects, so little time...
 

rain_darned_owl

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Normally I have an aha moment when I read DeeAnna's comments, but I am a bit lost here (note I haven't made liquid soap with KOH before):

"If you use citric acid in the sense of its being a chelator and not a neutralizer, then add the extra lye needed for the citric acid to react with --
10 g citric acid neutralizes 6.24 g NaOH.
10 g citric acid neutralizes 8.42 g KOH."

I am making bars of soap (NaOH) so are you saying to ...
1. add extra lye to compensate for adding citric acid as a chelator? or,
2. if your recipe calls for 6.24g of NaOH then you can add 10g citric acid as a chelator (and if you have more or less NaOH then do the math to figure out the amount of citric acid)
 

Susie

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If you have sodium citrate powder that doesn't need extra NaOH, when would you add it? While you are making the paste or at the dilution phase?
You add it at the paste phase.
 

Susie

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Normally I have an aha moment when I read DeeAnna's comments, but I am a bit lost here (note I haven't made liquid soap with KOH before):

"If you use citric acid in the sense of its being a chelator and not a neutralizer, then add the extra lye needed for the citric acid to react with --
10 g citric acid neutralizes 6.24 g NaOH.
10 g citric acid neutralizes 8.42 g KOH."

I am making bars of soap (NaOH) so are you saying to ...
1. add extra lye to compensate for adding citric acid as a chelator? or,
2. if your recipe calls for 6.24g of NaOH then you can add 10g citric acid as a chelator (and if you have more or less NaOH then do the math to figure out the amount of citric acid)
1. You add extra lye to compensate for the citric acid. You are making bars, so you would add 6.24 g of NaOH for each 10 g citric acid.
 

galaxyMLP

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Wouldn't sodium citrate be a problem since we are making potassium based soap? I would think it would act a bit like adding table salt where some of the soap (not a ton, but some) will salt out.

Susie, do you find after adding the SC your soap gets cloudier or it forms a separate layer?
 

Susie

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I have super soft water, so I do not personally use SC or CA.

However, since SC is not acidic, it will not affect the pH of your product. That is the primary benefit of using that rather than CA. No fancy fiddling with math, or worry about soap separating. You aren't going to use a great deal of it to worry about it salting out your soap.

And there is no reason to worry about it being a problem with KOH based soap. I have made liquid soap with up to 40% NaOH with no problem whatsoever. Again, the amount you are going to use is so small.

https://en.wikipedia.org/wiki/Sodium_citrate
 
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galaxyMLP

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Lucky you with the soft water! Sorry, I thought with the way that you worded your post that you did use it in your soap. My bad!

I understand that it wont need any neutralization but, I'm wondering if since its sodium citrate and not potassium citrate if it makes some sodium soap form and makes the soap cloudy or separates the newly formed sodium based soap from the water soluble potassium based soap. I don't think it would take alot to do that. I'll have to test it tomorrow!!
 

DeeAnna

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Rain -- here's an example that I hope clears things up for you. Say you have a recipe that calls for 100 g of KOH to saponify your fats. And you decide to also add 10 grams of citric acid to make citrate because you have hard water issues. To get that citrate made, the citric acid is going to use up some lye. You don't want it to use lye that is needed for saponification, so you will want to add extra KOH. The rule is 10 g citric acid neutralizes 8.42 g KOH, so you would need to use an extra 8.42 g KOH in this recipe -- this KOH is in addition to the KOH for saponification.

Total KOH = (KOH for saponification) + (KOH for the citric acid) = 100 g + 8.42 g = 108.42 g

***

Galaxy -- You have a valid point!
 

Susie

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Lucky you with the soft water! Sorry, I thought with the way that you worded your post that you did use it in your soap. My bad!

I understand that it wont need any neutralization but, I'm wondering if since its sodium citrate and not potassium citrate if it makes some sodium soap form and makes the soap cloudy or separates the newly formed sodium based soap from the water soluble potassium based soap. I don't think it would take alot to do that. I'll have to test it tomorrow!!
I have used KOH 60%:NaOH 40% recipes with no loss of clarity. If this is not what you mean by "sodium soap", then I apologize for misunderstanding, and could you please clarify?
 

galaxyMLP

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Really?? Very interesting!

I would've thought that the sodium soap would separate or at least make it get cloudy but it makes sense now. Both stay emulsified together. Thanks Susie!
 

DeeAnna

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I agree with Susie that sodium hydroxide doesn't necessarily cause soap to be cloudy or opaque. It's more the fats used (stearic, palmitic) and the solvents (water, alcohol, sugar, glycols, etc.) that affect clarity. Couple of examples -- I recently dissolved a grated up bar of olive oil (castile) soap in distilled water. I wanted to make a gel soap to use when wet-felting wool. I had made the original soap using only 100% NaOH, olive, and distilled water. The resulting gel isn't liquid -- it's more like firm Jello dessert -- but it is as clear as if it was a KOH-olive-water soap. The original Pears soap was an NaOH soap that was then dissolved in ethanol. The ethanol was allowed to slowly evaporate off, leaving a transparent soap behind.

But there's another aspect to the issue Galaxy wrote. The sodium may not be causing the problem; the citrate may be. I wrote on September 14th in the "Sodium citrate from baking soda and citric acid" thread about the same issue Galaxy is referring to -- adding sodium citrate to diluted LS DOES cloud the soap and cause separation. I don't have an answer to this issue, and I'm glad to finally hear I'm not the only one with the problem.

Here's what I wrote in Post 100 of that thread:

"I was wanting to use my homemade citrate to see how citrate controls soap scum created by mixing hard water from our well with my liquid soap. I wanted to add these results to the thread I started here: http://www.soapmakingforum.com/showthread.php?t=52456. Problem is, when I added the citrate to the water and soap solution, the citrate "broke" the soap so I ended up with scummy water that had a layer of fatty acid on the surface.

"Thinking perhaps I had an excess of citric acid still left in the solution, I added a bit extra baking powder to ensure the acid was fully reacted to citrate. Tried the test again. Same results. Added a bit of citrate solution to just the liquid soap -- no added water -- and the mixture of citrate and the (originally transparent) LS turned an opaque white.

"I'm stumped. My understanding has been that citrate works pretty well to chelate metals and reduce soap scum, and I haven't been hearing people complain about citrate "breaking" their soap. You other soapy chemistry geeks out there -- what am I missing? Suggestions and thoughts are most appreciated."

Source: http://www.soapmakingforum.com/showpost.php?p=544929&postcount=100

Edited 7 June 2016 to add -- I found the reason why my LS was turning white and separating when I added sodium citrate. I had made this citrate by reacting citric acid and baking soda to make a citrate solution. This solution also had excess baking soda in it, and it was the soda that was breaking down the soap. Sodium citrate without any excess baking soda (either bought commercially or made more carefully) works just fine -- no cloudiness and no separation.
 
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galaxyMLP

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So then maybe in this case it is acting like regular salt is when you add it to LS and some of it "salts out" at the top? I've neutralized my SC so I'll try it with mine tonight and see what happens. I made some paste the other day (not perfectly clear when diluted but, I'll be able to tell once I add the SC if there are any differences.)

Dee, we should also try making potassium citrate by the extra lye method and seeing if we get that same separation result If I get the same separation with my SC tonight.

I'll try tonight and report back. Would you like me to do it on the other thread or this one?

ETA: Ill try it w/ my castile recipe and also my new paste w/ palm, olive, shea and castor (its a little cloudy but not bad)
 
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DeeAnna

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Galaxy -- for me, continuing this discussion here in this thread is fine.

***
Geek Alert -- seriously nerdy chemistry stuff is coming up next! :)
***

Galaxy -- Some thoughts....

Could the baking soda and citric acid reaction be incomplete in that we don't have TRIsodium citrate, but instead a mix of tri-, mono-, and di-sodium citrate? In that case, the mono- and di- would act as weak acids in the diluted LS, similar to adding citric acid.

The pH of trisodium citrate ranges from 7.5 to 9.0 (0.1 M in H2O, 25°C). The pKa values for citric acid and its ionic forms are 3.138, 4.76, 6.401.

Or could our addition of citrate to the diluted soap, with its relatively low pH, be what's messing things up? Maybe we need to be adding the sodium citrate to the highly alkaline soap batter to force it to dissociate fully to Citrate 3- ion?

I'm a little outta my league here, to be honest, but this is what I'm currently wondering about. Any thoughts???
 
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DeeAnna

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Thanks, Coffeetime. It's your thread and I would respect your wishes if you don't care for the direction this sidetrack is going.
 

galaxyMLP

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You know, I thought about that briefly. That's why I kept adding baking soda until it didn't fizz any more and the solution was around a pH of 8. I'd like to try it with adding some more baking soda to reach a pH of about 10 and see if that makes a difference as well.

If we've got some mono and di sodium citrate that could definitely explain the cloudiness.

I'll try 3 things tonight then:

1. castile soap paste diluted w/ 2% added SC
2. palm/olive/shea/castor soap paste diluted w/ 2% added SC
3. castile diluted w/ 2% SC w/ added BS to make pH ~10
4. palm/olive/shea/castor diluted w/ 2% SC w/ added BS to make pH ~10

This will tell us if its the SC itself or if its the pH/the way we are making the SC. I want to try with both of my recipes to see if it makes a difference with the types of fatty acids too.

If none of those experiments results in a clear/unseparated/unchaged soap, I will make potassium citrate with my next liquid soap paste by the extra lye method.

ETA: Thank you coffeetime for allowing us to continue on your thread! We've hijacked it...
 
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