Is excess alkali the same as too high pH?

[BodyWasher]

Hi, I don't want to lick soap, but I want to know if there's excess unreacted lye in my soap. Is there any way to test this?

Is pH alone a good enough indicator? From what I've read, it sounds like the answer is no.

 

[AliensrReal]

pH is not a good indicator of excess lye. All soap will have a high pH.

 

[artemis]

You don't have to lick the soap:

Thread 'How To Properly/Safely Conduct The Zap/Tongue Test' How To Properly/Safely Conduct The Zap/Tongue Test

 

[BodyWasher]

@AliensrReal Soap with a pH of 9-11 I would assume is fine but a pH of 12-14 probably not. So it is somewhat helpful. That said, it sounds like even a relatively low (for soap) pH of 9 could have excess lye? I'm not sure.

@artemis those are instructions for putting soap on your tongue / in your mouth, which is what I'm trying to avoid.

 

[KiwiMoose]

@AliensrReal Soap with a pH of 9-11 I would assume is fine but a pH of 12-14 probably not. So it is somewhat helpful. That said, it sounds like even a relatively low (for soap) pH of 9 could have excess lye? I'm not sure.

@artemis those are instructions for putting soap on your tongue / in your mouth, which is what I'm trying to avoid.

Yes - you might test part of the soap with pH strips and find it is 10 for example, where-as somewhere else on the batch there could be a pocket of un-reacted lye. The best way to ensure you don't have unreacted lye is to use a soap calculator for measurements, and to ensure the lye is fully dissolved in the liquid before adding to the oils.
Unfortunately, the zap test will always require touching your tongue to the soapy liquid, so if you don't want to do that, you will never be able to perform that test. I liken it to when we were kids putting our tongues on batteries and getting a slight 'electric' shock. It's not scary at all. Nearly all soap will zap in the first 24 hours, but within a few days it will have fully saponified and no zap should occur.

 

[BodyWasher]

Ok, so I looked into this a bit more and there is an alternative! I would have to do an acid base titration. Dunn talks about it in Chapter 15 of Scientific Soapmaking. Compared to testing with my tongue, a titration is also a lot longer to complete and more complex.

I think I am just going to lick the soap like the thread @artemis recommended and have some apple cider vinegar after.

 

[artemis]

I think I am just going to lick the soap like the thread @artemis recommended and have some apple cider vinegar after.

Why the vinegar?

 

[BodyWasher]

Why the vinegar?

To neutralize the base. Same reason as you'd use lemon juice, it's a low pH.

I tried this apple cider vinegar, and ended up realizing mid-experiment that coffee is acidic too, so I switched to that. Edit: See @AliOop's post below. Neutralizing is an exothermic reaction and can intensify the burn, but at the small scales I'm playing with it was benign.

Quick update: I've licked 26 different bars of soap so far and only 2 have had this slow, spicy, stinging, bleugh, grossness. One of those was this recipe

• Liquid Coconut Oil 100.01g
• Lye (50% NaOH solution) 46.30g
• Water 23.14g

The .2315 NaOH SAP value was from soapcalc.net which seemed kinda high, and it crystallized on top.

Overall, it was gross, but not that bad. I had imagery of my tongue dissolving or getting caustic burns, and it was nothing like that.

 

[AliOop]

@BodyWasher you truly don't need to lick the soap. Instead, you can wet your finger, rub it on the soap, and touch just that fingertip to the tip of your tongue. You will have far less soap in your mouth that way. Plus, you don't want to end up blind.

Also, please don't use vinegar to neutralize excess alkali anywhere on your body, including your tongue. The acid will increase the exothermic reaction and thus make you more likely to suffer a burn. The SDS for lye says to use cool running water, so best to stick with that.

Of course, vinegar is great for cleaning up potential caustic spills on other (non-body) surfaces, but again, it will generate heat, which may or may not negatively affect that surface.

 

[BodyWasher]

@AliOop Haha, thank you. I did use the finger approach for the sketchy soaps. Tongue on bar only when I didn't feel any sensation after that.

That is helpful to know about acid increasing the exothermic reaction. I didn't know that. My experience lines up with that - using apple cider vinegar and/or coffee didn't give me an immediate soothing effect that I was hoping for (I was expecting something like milk after spicy peppers, not the case). At least I was right to rinse my mouth before trying to "neutralize". Anyway, the stinging sensation lasted mildly for about 2 minutes. Not much to fear.

 

[artemis]

Ok. If you keep saying "lick the soap" we're going to keep on assuming that you licked the soap and keep telling you that you don't have to do that. Most of us just call it the zap test.

 

[KiwiMoose]

Anyway, the stinging sensation lasted mildly for about 2 minutes. Not much to fear.

Now that you've done it, you'll see why it's no big deal. You don't burn your tongue off after all. lol

 

[AliensrReal]

Ok. If you keep saying "lick the soap" we're going to keep on assuming that you licked the soap and keep telling you that you don't have to do that. Most of us just call it the zap test.

I lick my soaps.

 

[AliOop]

Anyway, the stinging sensation lasted mildly for about 2 minutes. Not much to fear.

That's definitely not a zap - a zap is similar to being shocked with static electricity. It only lasts a milli-second, but you know it happened!

I lick my soaps.

Ok, now you're doggin' us. Gonna have to keep an eye on you.

 

[AliensrReal]

It’s the best way to know how they taste!

 

[melinda48]

Hi, I don't want to lick soap, but I want to know if there's excess unreacted lye in my soap. Is there any way to test this?

Is pH alone a good enough indicator? From what I've read, it sounds like the answer is no.

Maybe we need a “soap Lickers” decal! Ha ha ha ha

 

[KiwiMoose]

Maybe we need a “soap Lickers” decal! Ha ha ha ha

We have SLAs at work. I always thought they were Service Level Agreements, but now I realise they are Soap Lickers Anonymous!

 

[AliensrReal]

We have SLAs at work. I always thought they were Service Level Agreements, but now I realise they are Soap Lickers Anonymous!

I’m not anonymous. I’m just a soap licker.