Acetic Acid
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
Good luck getting solid KOH from an aqeuous solution. Its pretty damn hygroscopic.
|
|
|
hkparker
National Hazard
Posts: 601
Registered: 15-10-2010
Location: California, United States
Member Is Offline
Mood: No Mood
|
|
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.
My YouTube Channel
"Nothing is too wonderful to be true if it be consistent with the laws of nature." -Michael Faraday
|
|
|
Acetic Acid
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
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
National Hazard
Posts: 601
Registered: 15-10-2010
Location: California, United States
Member Is Offline
Mood: No Mood
|
|
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...
My YouTube Channel
"Nothing is too wonderful to be true if it be consistent with the laws of nature." -Michael Faraday
|
|
|
stygian
Hazard to Others
Posts: 242
Registered: 19-9-2004
Member Is Offline
Mood: No Mood
|
|
essentialdepot.com sells food grade in quanntity.
|
|
|
Stasis
Harmless
Posts: 7
Registered: 6-10-2010
Member Is Offline
Mood: Emulsified
|
|
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
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
| 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
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
"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
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
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
Super Administrator
Posts: 7976
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
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.
|
|
|
Acetic Acid
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1863
Registered: 18-6-2008
Location: Brittany
Member Is Offline
Mood: Dogs are pets but cats are little furry humans with four feet and self determination! 
|
|
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
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 95
Registered: 14-8-2011
Member Is Offline
Mood: No Mood
|
|
^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.
|
|
|
entropy51
Gone, but not forgotten
Posts: 1612
Registered: 30-5-2009
Member Is Offline
Mood: Fissile
|
|
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 10-11-2011 by entropy51]
[Edited on 10-11-2011 by entropy51]
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
Chemistry Alchemist
Hazard to Others
Posts: 403
Registered: 2-8-2011
Location: Australia
Member Is Offline
Mood: No Mood
|
|
I brought some reasonably pure KOH as pH changer... when i done the reaction with ammonium nitrate the reaction didnt go as planned but in the end i
got reasonably pure KNO<sub>3</sub>
[Edited on 11-11-2011 by Chemistry Alchemist]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
