Sciencemadness Discussion Board

Recrystallizing NaOH

Runningbear - 18-5-2010 at 17:12

Hi guys,

I have some caustic soda of unknown purity. The label says Caustic soda - great for soap making' Active constituent Sodium Hydroxide. So I'm guessing its pretty pure, however I'd like to recrysrallize it just to be sure.

What's the best solvent to use? Acetone?

mnick12 - 18-5-2010 at 19:05

Well,
As long as you NaOH is not some odd color than chances are it is fairly pure. It aslo depends on what you plan on using it for, most reactions can use technical grade materials without problems. As for recrystallizing NaOH I have a feeling that would be very difficult. And if for some reason you do decide to recrystallize it, I would not use acetone. Since there is a good chance you would get some junk from the acetone condensing with itself in the presence of the NaOH.


Anyway I hope that helps, and here are some things you may like:
Solubility in water 111 g/100 ml (20 °C)
Solubility in ethanol 13.9 g/100 mL
Solubility in methanol 23.8 g/100 mL
Solubility in glycerol soluble (from wiki)

rrkss - 18-5-2010 at 19:30

I'd leave it alone, unless you plan on doing the recrystalization under an inert atmosphere, the NaOH is going to react with CO2 in the air and convert to Na2CO3. Probably your primary impurity will be Sodium Carbonate from the reaction described above and some moisture that this hygroscopic chemical picked up from the atmosphere.

JohnWW - 19-5-2010 at 01:02

Unless the NaOH is totally dry, and opened and handled under dry and CO2-free N2 or Ar, it will not only absorb CO2 to form Na2CO3 and NaHCO3, but ALSO absorb H2O (being highly hygroscopic), which would enable it to react slowly with any glass used as a container, contaminating it with the soluble viscous polymeric silicate, Na2SiO3 ("water glass").

ScienceSquirrel - 19-5-2010 at 05:52

It is impossible to recrystallise sodium hydroxide due to its enormous affinity for water.
Industrially it is concentrated until all the water is driven off to produce molten sodium hydroxide.
This is then sprayed to produce prills or passed between rollers to form flakes.
If need some really up to the mark sodium hydroxide buy a new bottle! :o

bquirky - 19-5-2010 at 05:55

Hi is your costic soda per chance "Mechanix" brand ? in a white container with a red lid ? :)

just curious.

starman - 20-5-2010 at 05:43

Quote: Originally posted by bquirky  
Hi is your costic soda per chance "Mechanix" brand ? in a white container with a red lid ? :)

just curious.


Sounds like it from the decription.98% according to this.
Last lot of this I used left insolubles when dissolving in water.Not too flash.

Methansaeuretier - 24-5-2010 at 05:23

Maybe it's possible to recristallize it from ethanol. Na2CO3 and Silikates are insolouble in Ethanol but NaOH should be very solouble in hot Ethanol. So dissolve in hot Ethanol, filter and cool down in a closed flask.

not_important - 24-5-2010 at 07:59

Likely would not give good results. A standard purification route for KOH is to dissolve it in absolute EtOH, filter to remove carbonates, then evaporate in a silver dish followed by fusion to get the dry KOH; all under a CO2-free atmosphere. You just don't seem to get crystals, fairly strong heating seems to be needed as well.

A question that has not be asked is "what is the intended uses of the NaOH?" If it's just a simple base, then traces of carbonate are not a problem, in most cases a bit of chloride also isn't going to be trouble. Removing base metals is trickier, but again you need to ask if they will be harmful in your application.

A quick analysis of the product might be useful too, so that you get an idea of what's in it besides NaOH.

chief - 24-5-2010 at 08:15

In Ethanole ? I remember from a biodiesel-forum, that Ethanole + NaOH gives some "ethoxide" ...
==> This then is heated with the plant oil to give the biodiesel, some "... ethyl-ester" ...

nannah - 3-10-2014 at 05:14

I just wonder if the mr muscle draincleaner i have under the sink is pure NaOH? On the bottle it just say NaOH, but im not 100 % sure. And it doesnt say anything about it in its msds.

blogfast25 - 3-10-2014 at 10:03

Quote: Originally posted by nannah  
I just wonder if the mr muscle draincleaner i have under the sink is pure NaOH? On the bottle it just say NaOH, but im not 100 % sure. And it doesnt say anything about it in its msds.



If it's a clean, white product of dull looking prills with no blue stuff or aluminium chips in it, it's most likely to be 100 % technical NaOH.

For these applications it's simply not worth blending it with anything else, so your 'brand' is in all likelihood mass bought technical NaOH put in a fancy bottle.

[Edited on 3-10-2014 by blogfast25]

Praxichys - 3-10-2014 at 11:09

http://mrmuscledrano.com/au/our-products

If you have the liquid, it's some nasty gel with about 30% NaOH.

If you have the crystals, it's NaOH, NaNO3, NaCl and aluminum chips mixed together.

aga - 3-10-2014 at 11:50

Quote: Originally posted by mnick12  
Solubility in water 111 g/100 ml (20 °C)

How on Earth could that be measured ?

As soon as the NaOH hits the water, it wouldn't be 20 C anymore.

MrHomeScientist - 3-10-2014 at 11:57

Just let it cool back down to 20 C and see the 112th gram fall back out of solution, I presume.

aga - 3-10-2014 at 12:06

So whack in 1g, 2g ... 111g, each time allowing it to cool back to 20C, and see if it stays dissolved.

Smarts. Real Smarts.

That's why you're a Mr and i'm title-less.

MrHomeScientist - 3-10-2014 at 12:49

Hey, you're more of an International Hazard than I am! :)

blogfast25 - 4-10-2014 at 03:22

Quote: Originally posted by MrHomeScientist  
Just let it cool back down to 20 C and see the 112th gram fall back out of solution, I presume.


There's a better way, of course.

Add about 120 g of NaOH to 100 g of water and dissolve it in the absence of CO2 (use nitrogen or argon blanket for instance). As it dissolves, allow also to cool to RT, then stop stirring for a bit to allow solid NaOH to settle at the bottom.

Take a sample of the clear, RT supernatant liquid and titrate for NaOH (after sufficient dilution, of course!) This tells you the w% NaOH and from there the g NaOH/100 g water can be calculated.

Incidentally, preparing a 50 w% solution of NaOH is also a way to get rid of any Na2CO3 (provided you work in CO2 free atmosphere, of course) because the carbonate isn't soluble in the 50 w% NaOH. There's a phase diagram (NaOH/Na2CO3/H2O) on it somewhere.


[Edited on 4-10-2014 by blogfast25]

unionised - 4-10-2014 at 04:27

Before you try to purify NaOH, it's worth titrating some to see how pure it is already.

nannah - 5-10-2014 at 02:22

Quote: Originally posted by Praxichys  
http://mrmuscledrano.com/au/our-products

If you have the liquid, it's some nasty gel with about 30% NaOH.

If you have the crystals, it's NaOH, NaNO3, NaCl and aluminum chips mixed together.


My draincleaner is just white, to the naked eye. No aluminium bits or anything.

What can you do about it?



blogfast25 - 5-10-2014 at 04:00

Quote: Originally posted by nannah  
My draincleaner is just white, to the naked eye. No aluminium bits or anything.

What can you do about it?



It's probably unadulterated technical NaOH, 100 %. Verify this by titration with HCl, as unionised wrote.

semiconductive - 2-8-2018 at 20:16

I realize the thread is very old, but there is no data on the SciMaddness wiki on quantitative solubility of NaOH in glycerol. This makes me very curious, as I was told that glycerol and methanol are more acidic than water, so in theory -- NaOH ought to be able to react with them and release water. The data given earlier in the thread is incomplete:
Quote: Originally posted by mnick12  
Well,
Anyway I hope that helps, and here are some things you may like:
Solubility in water 111 g/100 ml (20 °C)
Solubility in ethanol 13.9 g/100 mL
Solubility in methanol 23.8 g/100 mL
Solubility in glycerol soluble (from wiki)


I've been trying to dissolve NaOH in Glycerol, just to test this idea out.
I'm having trouble getting even 1 molecule of NaOH to dissolve with 1 Molecule of Glycerol. eg: 10g glycerol + 3.36g NaOH.

So, if it does dissolve ... it does so very slowly. I've added 4g of urea to see if I can speed it up by adding another polar solvent, and NaOH seems to be dispersing finally; but it's cloudy (so like a colloidal suspension after an hour of stirring at 20C).

I came across a notebook saying that the actual solubility of NaOH is 1.9 parts per 100 parts Glycerol.
https://web.wpi.edu/Pubs/E-project/Available/E.../Glycerol_R...

That's very disturbing, after what I read about Glycerol.

According to several sites I've read, both methanol and Glycerol are more acidic than water; so that I would expect NaOH to be more soluble in them than water, and releasing water as a result of dissolution.

Glycerol (1,2,3-propanol ), I'm told has two -OH radicals that are more reactive than the third. I assume, by symmetry, that the 1,3 locations must be more reactive than the 2 position.

I am not sure which sites are more acidic than water, and if any are more basic than water. However, if even one is more acidic ... I would expect at least 3.36g of NaOH to dissolve completely.


Does anyone know if all three of the glcerol -OH radicals are more acidic (likely to give up H+) than water; or if Glycerol is similar to a zwitteron ... with one bond more positively charged than water (H+) and one more negatively charged?

eg: 2 propanol is more basic than water, which suggests that the OH on the center bond of Glycerol is likely a base as well. But I'm not sure how to tell for sure which Glycerol bonds are likely to chemically react with NaOH, and which bonds won't..

In Theory:
NaOH should dissolve in glycerol, release water; and the water could be boiled off leaving: eg: R-O-Na

If this is not true, why not?

GrayGhost- - 3-8-2018 at 14:39

Long time ago I preparate NaOH solution, for reaction between Sodium carbonate and calcium hydroxide and heating . Take the solution and put in bowl with lid and tiny hole for escape vapor and no intake air, for no reaction Co2 with hydroxide.

When liquid dry, only obtain a very thin film of Hydroxide, negligible quantity.:(