pH and experimenting

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alkelle

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So, I was pH testing my liquid soap with pH strips. I have never usedPhenolphthalein and was thinking about ordering some. I know you can find it in some pool stores but in rural IL there aren't a whole lot around so, I started looking online for pricing. Some how I ended up reading about Thymolphthalein which is another pH indicator. Phenolphthalein turns pink at about a pH of 8.3. Thymolphthalein will start to turn blue at about 9.3.

From what I've read a safe soap is below a pH of 10 so I'm going to try out the Thymolphthalein since it starts to transition at a higher pH. With that in mind I somehow ended up at an article about "Disappearing Ink." You know, that fun stuff you squirted on everyone you could to watch them freak out for a minute. Anyway, disspearing ink uses Thymolphthalein to make the "ink" blue. I ordered some disappearing ink to see if it will be a useful indicator in pH of soaps.

Another fun fact: they use NaOH in the disappearing ink to give it the blue color. (since it has a high pH and turns the Thymolphthalein blue) Anywho, when the drops leave the bottle and hit the air and the clothing, the pH level will drop below the 9.3 the Thymolphthalein needs to turn blue, thus making it "disappear." The website at the bottom also says you can use Phenolphthalein to make pink "disappearing ink."

My hypothesis: If I place a few drops on to the surface of soap (or in a liquid soap solution) it can indicate if the soap is in a safe range. While sitting on the surface of the bar, if the bar is below 9.3 it will turn clear, if it's above, it will transition to an appropriate blue color. Same for liquid soap, if it turns clear in the soap solution then we're good to go, if it stays a bluish tint might be on the safe side, stays a dark blue color, it's too high.

I ordered 24 1oz bottles from amazon for a little under $8. If my experiment concludes that it's acceptable then I'm definitely using it to test soaps since it's relatively cheap. If the experiment yields results that makes it unusable for testing soap then I'll have a lot of fun with the disappearing ink anyway. If you would like to read about how to "make disappearing ink" here is the link:

http://www.stevespanglerscience.com/lab/experiments/vanishing-ink

I will post after I conclude my experiment. If you have some disappearing ink lying around (yeah because that's a normal thing to have around the house) then please try and let us know what you come up with.

I would also love to hear everyone's thoughts, opinions, if they have any resource they'd like to share. :thumbup:
 

CaraBou

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Sounds like a lot more fun than a zap test! Anyone know when you can taste that?
 

Lin

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Do you mean taste in the zap test? If so, you aren't tasting a pH but "tasting" (quotes because its not a taste but rather a reaction) lye still in the soap. The pH will depend on the ingredients in the soap.
 

The Efficacious Gentleman

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There are soaps on the market above pH 10, so I am not convinced that anything over 10 is unsafe in the way that we would consider it to be unsafe.

Edit - that should say "I'm not convinced that EVERYTHING over 10 is unsafe"
 
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alkelle

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I still plan on zap testing my soaps. Zap testing tells you if there's free lye. The reason why it's like zapping your tongue on a battery is because alkaline batteries use KOH to carry the current. A soap can have a relatively high pH and still be safe (for people without sensitive skin) what makes it unsafe is the active lye and it's hard to test for active lye any other way than zap testing. I just want to know what the pH is because I have eczema and I get irritated by some soaps. I just want to experiment and see if it's a better way than phenolphthalein because phenolphthalein starts transitioning at a lower pH.

The differences between using disappearing ink and straight up Thymolphthalein is I'm starting with an already active transition so I'm waiting for it to go clear as opposed to waiting for it to turn colors.

I plan on testing the lye water, purposefully lye heavy hot process soap, cold process soap, and liquid soap as well as soaps I know are safe and testing it on things I know are below a pH of 9.3 like regular water. I have a lot of testing to do and I'll let you know what I come up with :)

Edit: I also plan on leaving the cap open on one of the bottles to force it to go clear so I can see if I can reactivate it and make it turn blue again on a high pH substance and then proceed to test that bottle as well on the lye water, the lye heavy soaps etc.
 
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Gaspar Navarrete

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If you want to estimate pH, the juice from the red cabbage make a better pH indicator than phenolpthalein, in my opinion. See this link for a complete description:

http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm

See this link for a picture of the color range of red cabbage:

http://images.flatworldknowledge.com/averillfwk/averillfwk-fig16_013.jpg

The cabbage juice changes to a wide variety of colors, making it easier than phenolthalein for one to discern the pH.

The red cabbage test and the zap test seem to be a good combination of tests. The general concensus is that the zap test is the best test.
 
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alkelle

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I also do the zap test.

However, the juice from the red cabbage make a better pH indicator than phenolpthalein, in my opinion. See this link:

http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm

The cabbage juice changes to a wide variety of colors, making it easier than phenolthalein for one to discern the pH.

I like to do a zap test and a red cabbage test. If both tests agree with each other, then it's a reassurance that I did not make a mistake with the testing.
I will look into that :) I'm just experimenting. So far I've diluted some of it in water and watched the blue disappear and added some NaOH and watched it turn blue again so it looks promising from where I stand. I have a lot more testing to do though. I'm already optimistic but anything can happen with experimenting. I plan on doing a lot more experimenting this weekend since I have a pretty full day tomorrow at ISU. Statistics, so useful but so many formulas. Ugh
 
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