PH level of soap

[DeeAnna]

"...The fatty acids are weak acids and NaOH is a strong alkali. Lets say that the NaOH "wins" over the fatty acids, and there are more OH in the final solution than protons, that is why the pH of the product is so alkaline. KOH is also strong, trietanolamina is weaker though but I have not tried myself..."

First sentence -- Yes, that's very true.

Second sentence -- Yes, the pH is alkaline. I'm not quite sure what "the NaOH 'wins'" means, however. In a properly made soap, there should be a stoichometric excess of neutral fats or fatty acids.

Third sentence -- Triethanolamine? Sure, you can use it to make soap. I'd love to hear more about your experiences with the soap when you make and use it. In the meantime, I really would like to connect with handcrafted soap makers who are making this type of soap and more data on how it performs. Would you provide that information, please? Thanks!

 

[Robert]

The pH of soap is alkaline because it is made from a strong alkali and a weak acid. In order to get soap with lower pH you should use weaker alkali.

You can do that, but it'll get you only so far. Neutrogena soap is made with triethanolamine (TEA) rather than lye. The solutions Neutrogena forms are less alkaline, with a lower pH, than are the corresponding solutions of sodium or potassium soaps. But despite its name, it's still not quite neutral. You can't get the pH of a soap solution too low before fatty acids come out of solution as fatty acids. If you understand what this means technically, Neutrogena is a buffer mixture with a pH around 8 IIRC, between the pKa of triethanolammonium ion and that of the fatty acids in the soap.

If you'd like to try making a similar soap, you can use TEA or ammonia. The trouble with using ammonia is that the product will still be alkaline enough to release ammonia gas and be stinky. Some mechanic's soaps are made with ammonia as part of their alkali, and I'm told they stink on purpose to "show how strong the soap is". TEA is less volatile, hence less stinky, although before neutralization it will like most amines smell like rotten fish; making soap with TEA in an unventilated facility would be unpleasant, I'm sure!

 

[DeeAnna]

"...You can do that, but it'll get you only so far...."

Yep. I agree, Robert. Thanks for the explanation from your point of view. I am also hoping to learn the poster's reasoning behind his/her suggestion to use TEA -- perhaps s/he has a perspective to offer that you and I are missing?

 

[Robert]

"...You can do that, but it'll get you only so far...."

Yep. I agree, Robert. Thanks for the explanation from your point of view. I am also hoping to learn the poster's reasoning behind his/her suggestion to use TEA -- perhaps s/he has a perspective to offer that you and I are missing?

I'm sure hir perspective is the same as that of the makers of Neutrogena. I don't know of any home soapmakers using TEA, but it would be interesting to know of. It may even be possible to saponify with TEA by an anhydrous process.

Theoretically it is possible to make soaps that give lower pH solutions by using extra fatty acid, just using the fatty acid-soap system itself as a single buffer. I don't know whether that happens normally with superfatting. The other Bob the soap expert said he thought that even in cold process, the extra fat is hydrolyzed into fatty acid & glycerol rather than being present as glyceride in the final product. In a soap with excess f.a. theoretically the buffer formula would apply:

pH = pK - log([f.a.]/[soap])

But I have my doubts that it would come out that close to the model, given the very non-ideal solution characteristics of soap. With TEA soap, though, I'm sure there would be effective buffering.

 

[Jakeedin]

danielle22033. Up and until recently, I was really alarmed with myself when it came to pH levels. When I first used litmus strips, I found it difficult as it often gave me the impression 8.0 to something safe. Then I remembered that I was slightly colour blind so, I got myself a pH meter.
It was only until I have tested the soaps on myself and with my friends that I have come to accept that in CP soaps pH is usually in the bracket of 9.5 to 11.0, 10.5 and 10.0 is very normal even after curing. The important factor to me now, is the ingredients and how it would benefit the skin that matters to me most.

 

[verotxu]

Hello!

I have been away for the weekend and unable to connect to the forum.

As i have earlier posted I have not used myself TEA for making soap, I just got the info from a book about scientific book about cosmetics. I did not mean that you were able to get a soap with the same pH value of the one of the skin. I just said that you could lower the pH using a weaker alkali.

Going back to the scientific debate. Soap is a salt made from a weak acid and a strong base. The soap will dissociate into a cation and an anion when it will be in contact with water. The cation (Na) comes from the strong base and consequently it will not have the strengh to react with anything. On the contrary the anion comes from a weak base and it has the strenght to react with water and produces OH which increases the pH of the solution.

If the acid is stronger than the alkali, then the resulting pH of the soap will be acid; if the strenght of the acid and the base is equal the resulting pH will be neutral.

Cheers

Veronica

 

[lhaase0217]

PH Levels in Soap

After reading a thread and some odd posts, I am gathering that using PH test strips, or to test the PH levels, are basically a waste of time when a zap test is sufficient.

That being said, I still like to put the PH level on my labels for label appeal. I have used the test strips and found I received levels from 7.5 to about 9.5. This is satisfactory for me. I do want to invest in a PH meter sometime in the future.

I have found that using milks in your soap helps to lower the PH level, at least it did in my cupcake recipe. I made 3 batches, 2 with 1/2 water mixed with lye and 1/2 cold GM added to oils before lye/water solution; and the last with only water with the lye.

When I tested the batches, the 2 with GM were about 1.5 to 2.0 lower in PH value than the ones made with no GM.