Sciencemadness Discussion Board

storing highly concentrated sodiumhydroxide

benzeentje - 6-4-2012 at 10:04

Hi all,
I bought Vogel's textbook of quantitative chemical analysis the other day, and it says that you can make carbonate-free NaOH from very concentrated NaOH solution (the carbonate precipitates out then).

While I was overthinking this, I was asking myself what the best container would be to store this highly concentrated (50/50m%) NaOH solution in. From what I know of NaOH, it reacts with glass (altough very slowly) so it is best kept in PP bottles. But I don't have PP botles at home. I have however PET, but I read on your forum that PET and NaOH reacts to terephtalic acid when heat is applied.

Does this reaction also happens at room temperature? Should i keep this in a glass or PET container?

blogfast25 - 6-4-2012 at 12:24

Use clean HDPE containers. PET will hydrolyse somewhat.

peach - 6-4-2012 at 13:12

HDPE

Glass is easy to crack so you may as well only use it for things that aren't compatible with HDPE; e.g. some volatile organic solvents tend to soften / extract plastics.

Strong NaOH / KOH solutions do slowly attack glass; the QuickFit catalogue mentions it in the first few pages. I've also watched one of my sinters fall apart in a strong solution of KOH.

HDPE is second only to PTFE in terms of it's spectrum of chemical resistance. But PTFE bottles are somewhat pricey.

neptunium - 6-4-2012 at 15:26

bottom line is PTFE is THE best long term chemicals storage cold and warm climate.
why o you need such a high concentration of basic solution? glass performs very well with 10 % or 1N concentration....??

DerAlte - 6-4-2012 at 21:10

@benzeentje
DATA SOURCE FOR NaOH SOLUTIONS, ETC

You may find the following useful:
OxyChem Caustic Soda Handbook
http://www.panaceauniversity.org/NaOH%20Hand%20book.pdf

Also search for Solvay caustic soda under product characteristics. There is a graph there that shows the solubility of NaCO3 in strong NaOH solutions. At a concentration of 500 g/kg the solubility drops to around 1g/kg. I have personally tried this qualitatively and noted this. Yet at c=300g/kg the solubility is at least ten times greater.
This is similar to the almost total precipitation of NaCl by passing HCl into a solution. The probable reason is that the activity coefficient for NaoH rises very rapidly in the region, enhancing the common ion effect.

I agree with all the above regarding materials for container and add HDPP is also good.

Regards
Der Alte

benzeentje - 7-4-2012 at 02:29

Quote: Originally posted by DerAlte  
@benzeentje
DATA SOURCE FOR NaOH SOLUTIONS, ETC

You may find the following useful:
OxyChem Caustic Soda Handbook
http://www.panaceauniversity.org/NaOH%20Hand%20book.pdf

Also search for Solvay caustic soda under product characteristics. There is a graph there that shows the solubility of NaCO3 in strong NaOH solutions. At a concentration of 500 g/kg the solubility drops to around 1g/kg. I have personally tried this qualitatively and noted this. Yet at c=300g/kg the solubility is at least ten times greater.
This is similar to the almost total precipitation of NaCl by passing HCl into a solution. The probable reason is that the activity coefficient for NaoH rises very rapidly in the region, enhancing the common ion effect.

I agree with all the above regarding materials for container and add HDPP is also good.

Regards
Der Alte


Is this the graph you are referring to? http://www.solvaychemicals.com/Chemicals%20Literature%20Docu...

Thanks for the very helpfull manual, if I understand well I don't need 50%m/v, but 25%m/v is good enough. Also, the graph says if I cool the solution, the solubility decreaser even further, right?

DerAlte - 7-4-2012 at 09:42

@ benzeentje

In answer to your questions, yes and yes.

neptunium suggests that glass is probably OK for up to 10% solutions and I'll second that. At 25%, however, long term some etching will be seen. In most uses the silicate produced will not really matter; carbonate is the problem.

Never trust a NaOH/KOH solution without recalibration.

The main thing with solutions (and solid) alkaline hydroxides is to exclude air by a tight fitting seal (hermetic, if possible). Solid NaOH avidly takes up water and carbon dioxide from the air; solutions absorb the CO2.

If you have an unknown alkaline hydroxide KOH never produces the feathery crystals of Na2CO3 or NaCO3.H2O that NaOH does on the sides of the vessel and the surface because K2CO3 is far more soluble. KOH merely liquifies.

Regards
Der Alte

blogfast25 - 8-4-2012 at 05:49

Quote: Originally posted by DerAlte  

If you have an unknown alkaline hydroxide KOH never produces the feathery crystals of Na2CO3 or NaCO3.H2O that NaOH does on the sides of the vessel and the surface because K2CO3 is far more soluble. KOH merely liquifies.


Doesn’t the link to the Solvay figures for the NaOH-Na2CO3-H2O system contradict that, at least for low concentrations of NaOH where Na2CO3 solubility is still very high? By ‘on the sides’ did you mean inside or outside of the vessel?

Funny thing is, when I dissolve NaOH (small prills) to a 0.1 M solution I have sometimes observed small amounts of ‘feathery’ crystals floating around. No idea what they are and the quantity is really too small to try and isolate them.