phenolphthaline test

[LyeSoap]

So I ordered 1L of phenolphthaline 1% solution to test the pH level of my soap. I'm not really sure how to use it. I took a small shaving of my batch, put it in a bowl and applied a few drops of the solution to the soap. As far as I could see the liquid didn't turn pink, I even used a q-tip to see if there was a tint of pink on it... There was nothing.

I don't know why but I added a bit of water and it lit up like the fiery eyes of bill murray in life aquatic. Anyways, what is the correct way to use this? The book says a few drops on the soap should be proof enough, but the pinkness when I added water brought me here.

 

[Guest]

I have no experience with it but I googled this:

http://www.newton.dep.anl.gov/askasci/c ... m00704.htm

"My soap making experience has been with fairly large (hundreds to thousands of gallons at a time) batches. For testing, try dissolving 10 grams of soap (about a tablespoon) in 2 ounces of a water/isopropanol solution [Prepared by mixing 3 parts by volume of 70% isopropyl alcohol (rubbing alcohol) and one part of distilled or R.O. water. This 50/50 solution efficiently dissolves soap and caustic, but not free oils/fats] Test this solution with phenolphthalein. If the color is dark pink and the solution clear, you have excess caustic - add a little more oil and cook your batch some more. If it is colorless to yellowish but clear, your pH will be fairly neutral. If it is hazy, you have unreacted oil that you may want to cook away with caustic. If it is hazy AND pink, it is not done reacting yet - cook it a little while longer and retest."

The full article is much, much longer and I suggest you read the whole thing.

 

[LyeSoap]

Thanks again for your help Lovehound. The book recommends phenolphthalein, but once its gone I'm going to stick with test strips.

 

[LyeSoap]

Just an update on this method:

I used it and it appears that my soap is no longer caustic. The distilled water / alcohol combo yielded a clear solution on both my first and second batch. I'm going to take this as a sign of it's neutrality.

Not too sure why the phenolphthaline will turn pink to normal tap water but I'm going to try using my soap anyways and see what happens. Perhaps its the chemicals from the hydro company that are turning it pink. If thats the case it makes me not want to drink the stuff...

 

[abassa]

Did you check the PH of water, maybe the water itself is basic (has excess OH (hydroxide ions) which is very possible, that will cause the formation of the pink color. you can try adding a drop of phenolphthalene into the soap directly (just take a pea size soap piece) without dissolving it in water.
one way to check the PH of water is to add one drop of phenolphthalen(phen) into one drop of water if the colorless phen becomes pink, it is the water that causing that