Potassium Hydroxide 10% Solution (30 mL) - Amazon.com

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Author: Subject: Possible OTC Potassium Hydroxide? Acetic Acid
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posted on 25-10- at 14:05 Possible OTC Potassium Hydroxide?


http://www.atlantishydroponics.com/TDS-and-pH-Calibration-So...

Tell me what you think of this. It's obviously a liquid solution, but it's stated as food grade and should be extremely easy to get solid KOH from this. However, it costs a bit and it would take me 40 minutes to drive there from where I live. Does anyone have any experience with this product or similar hydroponics supplies? Thanks Acetic Acid
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posted on 25-10- at 14:13

I already have Rooto at my disposal, but the same store claims to sell a gallon of food grade sulfuric for 24.99 as pH down. DJF90
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posted on 25-10- at 15:43

Good luck getting solid KOH from an aqeuous solution. Its pretty damn hygroscopic. hkparker
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posted on 25-10- at 15:50

Maybe, but it would be cheaper to just buy it dry like this:
http://www.dudadiesel.com/choose_item.php?id=2drhdp

NO need to boil down and cheaper.



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posted on 25-10- at 16:08

Yeah but that's only 90% pure :/

As for the hygroscopic comment, I totally forgot about that. I think it's possible to boil it without decomposing though. hkparker
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posted on 25-10- at 17:09

Do it in a stainless steel container, it will attack glass. Didn't realize that KOH was 90%, sorry. There are other stores though.

http://secure.sciencecompany.com/Potassium-Hydroxide-500g-P6...



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posted on 25-10- at 17:16

essentialdepot.com sells food grade in quanntity. Stasis
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posted on 26-10- at 03:44

Quote: Originally posted by Acetic Acid  Yeah but that's only 90% pure :/

As for the hygroscopic comment, I totally forgot about that. I think it's possible to boil it without decomposing though.

I think you'll find 90% is very good as far as purity is concerned, 85% is standard. blogfast25
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posted on 26-10- at 04:18

The streets of eBay are paved with sellers offering biodiesel KOH at cut throat prices. 'pH up' KOH is premium priced because it's branded. Extracting KOH from a solution is very hard w/o turning it into potash.



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posted on 26-10- at 05:28

Quote: Originally posted by Stasis   Quote: Originally posted by Acetic Acid  Yeah but that's only 90% pure :/

As for the hygroscopic comment, I totally forgot about that. I think it's possible to boil it without decomposing though.

I think you'll find 90% is very good as far as purity is concerned, 85% is standard.

That's right. There's usually about 10 - 15% water in solid KOH, no matter how hard you try to remove it. It's just that hygroscopic. So that sounds like excellent purity to me! Acetic Acid
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posted on 31-10- at 07:19

"Extracting KOH from a solution is very hard w/o turning it into potash."

As in, if I heat the solution, it will react KOH + CO2 -> K2CO3? That would make sense.

If I want to use a desiccator bag to try KOH, I'm pretty sure that won't work. The KOH I'm trying to dry would actually be even more hygroscopic than the CaCl2 I usually use for that. Essential Depot seems the way to go. Acetic Acid
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posted on 8-11- at 07:00

I was trying to titrate Rooto with school KOH. When I got values such as 20.0 and 20.2M, I realized that the KOH was causing problems. I concluded that when I originally weighed the KOH, it had about 12% water in it, making me think that I was using more KOH than I was in the titration. When I used a stock solution of NaOH for the same titration, I got a more realistic 17.8M for my Rooto. woelen
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posted on 8-11- at 23:33

Yes, KOH, even stuff obtained from chemical supply houses to be used as reagent contains at least 10% of water, frequently even 15%. KOH already is called reagent grade if it has a purity of only 90%. Of course, it only is called reagent grade if besides water there only are trace amounts of other impurities.



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posted on 9-11- at 04:01

Would NaOH be the same way? It's also hygroscopic and it also absorbs CO2. If so, how can you accurately standardize a base solution? ScienceSquirrel
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posted on 9-11- at 04:14

Sodium and potassium hydroxide solutions are made up using the appropriate factor to allow for contained water. They are then standardised against a standard acid solution.
They are not primary standards because they absorb water from the air, carbon dioxide can be ignored for most practical purposes if the solutions are made from fresh material and stored in sealed containers. DJF90
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posted on 9-11- at 04:20

Further to SS's comment above, standard acid solution is typically Potassium hydrogen phthlalate, or Sulfamic acid (if it has been rigorously purified - I'm certain this is detailed in one of the volumes of Inorganic Syntheses) Acetic Acid
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posted on 9-11- at 05:59

^Don't have either of those. I do have:

Hardware store HCl (~10.2M)
Rooto H2SO4 (~17.8M)
Glacial CH3COOH (17.5M)
Phosphoric acid (?)
Formic acid (?)

Please advise.

Hardware store HCl can be diluted to about 20% HCl and then distilled to obtain constant boiling acid of very accurately known concentration which depends on the barometric pressure during the distillation.

A carefully measured mass of the constant boiling distillate can then be accurately diluted to provide a primary acid standard of known normality.

This is well described in the literature and has been discussed here.

Once you have your standard HCl solution you can standardize a base solution such as KOH by titration.

Briefly, the hardware store acid should be diluted to a density of about 1.096 and distilled until a constant temperature of the vapor passing into the condenser. The constant boiling distillate is collected. As a specific example, if the barometric pressure is 760 Torr, the distillate will contain 20.22 % HCl by weight. 18.02 grams of this distillate carefully diluted to a total volume of 100 mL will be an accurate 1 Normal (1 Molar) solution.

[Edited on 10-11- by entropy51]

[Edited on 10-11- by entropy51] blogfast25
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posted on 11-11- at 04:53

I currently use twice recrystallised, anhydrous sodium carbonate as a primary base standard and twice recrystallised, anhydrous oxalic acid as primary acid standard, both kept in dessicator. My titrations of commercial vinegar, 36 % HCl, 95 % H2SO4 and weak ammonia have yielded values in line with 'what's on the tin'. I weigh to 1 mg.

I've also used the titrations to determine yield of HCl and NH3 generators and to make simple buffer solutions.

Another standard I came across in a booklet by Metrohm (the 'robotitrator' suppliers) was TRIS buffer material but I haven't used that one yet.

And if anyone here fancies a kind of Round Robin, I'm up for it.