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Discussion in 'Lye-Based Soap Forum' started by n6561echo, Feb 14, 2020.
What should the pH of CP soap be after 4-6 weeks?
Most handmade cp soaps will cure out to be a pH level of anywhere between 9.5-11. It will all depend on the recipe/oils used.
I would not be concerned about pH. I would be more concerned if the soap is lye heavy or not. If it is lye heavy, the pH may still be an acceptable range for soap. I've made soap that tested "around" 11 but I had intentionally made it lye heavy and it still zapped.
At pH 11, I would expect you would get a "good" zap. If the rational for using a SF of 5-8%, is to assure there is NO EXCESS OF LYE, then I would expect a pH closer to 7 or 8, and very little free Na to combine with CO2, and thus NO SODA ASH! Am I correct that the NaOH hydrolyzes, resulting in free sodium, and OH to combine with the fatty acids?
Cold process soap is alkaline, typically 9-10, although pH may go as high as 12, or as low as 8 - anything less than 8 is not soap. (Or an incorrect pH result due to incorrect testing methods). So... no you can have soaps that test at pH 11 or 12, but do not zap because they are not lye heavy.
The real question is... why are you testing pH? Is it to check for lye heaviness? If so, then pH is horribly inaccurate, difficult to test correctly, and misleading to determine if soap is lye heavy or not. To test for lye heaviness, please use the zap method. You can find a how to in the beginners section (it should be a sticky).
pH in soap is never ever below 8 for HP or CP.
If it's NOT and excess of free, unreacted hydroxyl ions (OH), from the dissociation of the lye (Na+OH), then what accounts for the high alkaline pH?
In addition, if "soda ash" is NaCO2, then the Na ions must have been free to combine with the CO2 in the air. CO2 CAN'T combine with the NaOH molecule!
Indeed, in fact, I think I may have padded the bottom number erroneously. Looking through notes, I have 9 as the lowest pH, not 8. Once soap pH gets lower than soap likes to be, I believe it will separate back into fatty acids. (Or... ahem... that's what my notes say... I can't speak from personal experience.)
I'm also going to mention, as long as I have my notes handy, that the intentionally lye heavy soap that I made was tested with pH strips, and my notes say "the color could be 10 or 11, assume 11 for worst case. zapped like a mofo". This particular soap is also noted after a 6 month cure to still be a "10 or 11" pH but no longer zap. This was my coconut and bacon grease soap, which was why I intentionally made it lye heavy, to make sure the bacon grease did not go rancid. It was completely experimental on my part and not recommended for regular soap practices. (Although the soap was wonderful after the lye cured out.)
You're talking way smarter than I am... so I'm afraid that I can't help you with the question in the way that you have formed it. You'll have to dumb it down for us normal folks.
You haven't answered my question if you are wanting to use pH to test for lye heaviness, or what your intention behind testing pH is.
@amd lol, you're hilarious. I actually lol when I read your post.
But you might be right , the lowest it could be is either 8 or 9 ... I always forget ... probably because I never both to check anymore. If it doesn't zap, it's done.
@n6561echo - I'm sure one of the chemists on the site will respond to your question in more scientific terms. But "true" soap (made with oils/lye) will never have a low pH as amd pointed out. Once it hits a certain level, it separates and is a big mess rather than soap.
Not sure why you thought EXCESS LYE would prevent Rancidity! Rancidity is 1) complete, or incomplete OXIDATION (by oxygen free radical) of the double bonds in mono and poly UNSATURATED FATTY ACIDS, or 2) HYDROLYTIC rancidity which occurs when triglycerides are hydrolyzed releasing free fatty acids and glycerol. Either reaction results in the production of the short-chain fatty acids that are responsible for the malodorous smell we experience rancidity). In either case, the addition of an ANTIOXIDENT (vitamin E) would have been more appropriate.
Probably because she is not a chemist as she has already (nicely) declared.
... and now you're just trolling to start arguments.
But I will answer your question. Making a soap intentionally lye heavy means there is more base (lye) than acid (oils) in the acid+base=salt formula that we know creates soap. Thus there are no extra oils in the soap left to become rancid.
I am not, but I know two of them IRL... one of them is sitting next to me as I type.... so there's that.
Actually, I'm more interested in PREVENTING SODA ASH. If it is, in fact the reaction of unreacted lye with the CO2 in the air
(Na + CO2= Na2CO3), then there must be an EXCESS of lye in the batter. It seems like adjusting the chemistry (PREVENTING IT) would be a
better plan. Reducing the alkalinity (dryness, and irritability) as much as possible, is my goal.
To be honest, I don't get soda ash, I do hp and soda ash is a cp issue that I have not experienced yet.
Don't we SF so that lye soaps are as NON DRYING, and NON IRRITATING, as possible? Not sure that I would want to use a LYE HEAVY soap, but that's just me.
VERY INTERESTING!!! Are you saying that "soda ash," the dread of CP soap makers, is NOT an issue for HP soap makers? Any idea why???
As far as I am aware, yes that's what I'm saying. I haven't seen it yet. But maybe I've just been lucky. As to why, I have absolutely no idea. Never had a problem with it, so never worried about it and haven't bothered to research it as I have too many others things to research right now.
My ultimate goal is to reduce soda ash in CP soap! If unreacted lye, is the basis for soda ash, that seems like an obvious candidate for exploration.
Thanks Kcryss. I feel like Colombo, just one more question. Having never made HP soap, I guessing that I can't do all the fancy swirls and complicated patterns/CP soap, but I can add clays, colors, and fragrance (EO,FO). And, of course, here's the second question. Is HP soap "harder" and "longer
lasting than CP soaps?" Thanks again for your input and time.
I'm still very new, but will answer the best I can. Maybe others with more experience will chime in when they get a chance.
It takes some practice to get the process down enough that you can actually get the fluidity needed for swirls. However, that being said, yes it is very doable. It still doesn't look as creamy and smooth as CP but is still very nice looking in it's own right. I guess the best way to put it, is that it has more rustic natural look.
With proper cure time, both CP and HP will get hard and last an equal amount of time. It also very much depends on the recipe. Some oils/combinations make softer soap. Most people on here use sodium lactate to increase hardness, especially when using more of the softer oils.
I use clays, herb infused oils etc. just like CP, but most of what I add is after the cook. I prefer adding after the cook because there is less chance of chemical changes occuring once the lye and oils have saponified.
What you want to be true about soap and what is really true are two different things. You will not find a functional soap with a pH of 8 or less.
The normal pH of soap with no excess lye is between 9.5 and 11 give or take, as others have mentioned above. The exact pH will depend on the fatty acids in the recipe. Properly made soap will indeed be quite alkaline but will not zap.
"...Am I correct that the NaOH hydrolyzes, resulting in free sodium, and OH to combine with the fatty acids?..."
You are misinformed. Sodium hydroxide (NaOH) dissociates; it does not hydrolyze. The sodium ion (Na+) reacts with the fatty acids to make soap. The hydroxide ion (OH-) reacts with the glycerol backbone of each fat molecule to form glycerin.
Your FREQUENT use of ALL CAPS gives the effect of a person who is shouting or pounding the table. Do you intend to create the impression that you are SHOUTING?
You are correct that NaOH "dissociates (spreads apart), as a result of polar forces within the water (hydrolysis). Yes, the Na ion combines with the fatty "acid" to form a "salt" hence the chemical name used on soap and cosmetic labels. As I said before, my goal is to understand, and reduce/eliminate soda ash and the thick clay like coating, forming on my CP soaps. Adjusting the chemistry should be easier & more reliable, than eliminating the CO2 exposure. Maybe NOT! Ooops. NO I'm not shouting. Think of it as quiet emphasis. But, your point is well taken; I'll stick to quotation marks (whispers of emphasis). Thanks for your input.
Separate names with a comma.