pH greater than 14, diluting, homemade lye, etc

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passedpawn

passedpawn

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A few of questions here:

1) If I have a solution who's pH is greater than 14, how to do I measure this? Can I just dilute with distilled water by 10x and expect the pH to come down one full digit? My meter won't go above 14 (perhaps none do).

2) I calculated that a 33% KOH solution would be pH 14.77.
  • 1L = 1000g
  • KOH = 56g/mol
  • 33% solution = 330g/56g = 5.89M
  • pH = 14+log(5.89)
  • pH = 14.77
3) will measuring high pH (including > 14) damage, or accelerate the demise, of my pH electrode? I ask because after doing some measurements yesterday, it's now blinking "renew", which means replacement time.
 
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Dilution by 10X will bring the pH down by one point. As stated above, safety equipment is a very good idea.
 
passedpawn said:
A few of questions here:

1) If I have a solution who's pH is greater than 14, how to do I measure this? Can I just dilute with distilled water by 10x and expect the pH to come down one full digit? My meter won't go above 14 (perhaps none do).

2) I calculated that a 33% KOH solution would be pH 14.77.
  • 1L = 1000g
  • KOH = 56g/mol
  • 33% solution = 330g/56g = 5.89M
  • pH = 14+log(5.89)
  • pH = 14.77
3) will measuring high pH (including > 14) damage, or accelerate the demise, of my pH electrode? I ask because after doing some measurements yesterday, it's now blinking "renew", which means replacement time.
Click to expand...

Sounds like @passedpawn is getting serious about his keg cleaning! :eek:
 
JimRausch said:
I thought that pH only goes from 1 to 14. Trying to remember from my chemistry classes of almost 40 years ago......
Click to expand...

It can go above 14. The henderson hasselbalch equation is 14 = pH + pOH, where "p" is the -log(). Rearranging, pH = 14 - pOH, or pH = 14+log(OH-). If the OH- molarity is greather than one, pH can go above 14. For example, if you mix 560g of KOH into a liter of water, you get a 10M solution, and the pH would be 14+log(10) = 15. At least that's how I think it works. In fact, since there are 55.5 mol of H2O molecules in a liter of water, you could put 55.5M of KOH in there (KOH+H2O->KO+H3O) and you'd get a max pH of 15.74!

It can also go below zero.

I'm no chemist, but I've got my college chemistry books right here and I feel empowered :) and probably wrong.
 
Silver_Is_Money said:
Dilution by 10X will bring the pH down by one point. As stated above, safety equipment is a very good idea.
Click to expand...

I strained water through many buckets of ash from my fire pit (burned a lot of oak over the last few days). It should have KOH of some concentration in there. By sheer bad luck (or perhaps causation), my pH meter decided to crap out on me. New electrode will be here in a few days.

My intent was to boil down to 14.77pH, but without a pH meter I decided just boil a bit of it down to a solid. Just did that an hour ago.
 
passedpawn said:
I strained water through many buckets of ash from my fire pit (burned a lot of oak over the last few days). It should have KOH of some concentration in there. By sheer bad luck (or perhaps causation), my pH meter decided to crap out on me. New electrode will be here in a few days.
Click to expand...

BTW, this didn't work the way I had hoped. I think the fluid out of the ash was water and potassium carbonate (K2CO3). I think there's a path forward to convert this to the KOH (potassium lye) that I want, but I'm already in over my head and frankly if I have to buy lime at the store I might as well buy the lye, my ultimate goal, in the first place.

Pretty much a fail on my part.
 
bracconiere said:
maybe this would help, it says to smoke the carbonate to make oxide, then react that with water......i think, i didn't finish...

https://sciencing.com/make-potassium-hydroxide-5700913.html
Click to expand...

I did end up boiling it down to a powder. Man, that stuff (whatever it is) was super-hydroscopic... a day later that powder is in a thin liquid form again, absorbing H2O from the air.

My new pH electrode comes in today, so maybe I'll titrate with HCl (actually muriatic acid that I have on hand) and figure out the OH- concentration I have here.
 
passedpawn said:
My new pH electrode comes in today, so maybe I'll titrate with HCl (actually muriatic acid that I have on hand) and figure out the OH- concentration I have here.
Click to expand...
That's really the way to do it. pH isn't going to tell you much as even if your meter reads pH > 14 I wouldn't put a lot of confidence into such a reading. pH respond to sodium as well as pH at such high levels, for example. Since pH is -log of the activity of hydrogen and hydrogen ion activity is so low at pH near 14 I don't have much confidence in one's ability to determine OH- concentration from a pH reading. But you can easily determine what it is by titrating with acid. With a strong acid (such as HCl) the calculation becomes trivial.

I assume your interest in doing this is to determine the alkalinity of your rather than the OH- ion in particular. If the pH is close to 14 then clearly OH- is going to be the major contributor to it.
 
ajdelange said:
That's really the way to do it. pH isn't going to tell you much as even if your meter reads pH > 14 I wouldn't put a lot of confidence into such a reading. pH respond to sodium as well as pH at such high levels, for example. Since pH is -log of the activity of hydrogen and hydrogen ion activity is so low at pH near 14 I don't have much confidence in one's ability to determine OH- concentration from a pH reading. But you can easily determine what it is by titrating with acid. With a strong acid (such as HCl) the calculation becomes trivial.

I assume your interest in doing this is to determine the alkalinity of your rather than the OH- ion in particular. If the pH is close to 14 then clearly OH- is going to be the major contributor to it.
Click to expand...

Yes, I think all I care about is total alkalinity in solution - I don't think I care what form the bases are. At least, I hope that's the case in saponification. This is a awkward attempt to make soap from stuff that I can find in my back yard (ignore the fact that I don't have fatty animals roaming back there).
 
I believe I've read somewhere in my distant past about concentrating the ashes derived KOH solution only until an egg floats upon it. I don't think this requires achieving or exceeding pH 14. Likely more on the order of 11-12 pH is achieved via this method.
 
Silver_Is_Money said:
I believe I've read somewhere in my distant past about concentrating the ashes derived KOH solution only until an egg floats upon it. I don't think this requires achieving or exceeding pH 14. Likely more on the order of 11-12 pH is achieved via this method.
Click to expand...

1.080. I did a bunch of research many years ago when I heard that brewers know they had a big beer when an egg floated in the wort. Turns out that the average specific gravity of a fresh egg is about 1.080. I did some calculations a few days ago and I think, for KOH, I'd need something closer to 1.300 for the alkalinity I'm looking for. BTW, a floating potato is apparently a similar test, as is dissolving a bird feather.

That's not to say you couldn't make soap with the lower value. Not sure where this experiment will end up (garbage), but I'm going to continue to attempt to get the higher alkalinity.

full
 

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