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Topic: Obtaining a hot NaOH solution  (Read 11188 times)

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Offline BlueTheCow

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Obtaining a hot NaOH solution
« on: September 05, 2007, 10:27:50 PM »
How can I obtain (or I guess "create") a hot NaOH solution (150-200ºC) without boiling off all the water?

I tried placing 2g NaOH in a small stainless steel cup (I think it was supposed to be used as some sort of measuring cup) and pouring on 5ml tap water (all at about 26ºC). It dissolved and increased in temperature to about 50ºC (it was difficult to get accurate readings quick enough, given the relatively small amount of material and my slow thermometer, but it stayed under 55ºC). I then put it on an "Electric Burner" and heated it to about 150ºC. My goal had actually been to heat it to 180ºC to test it on something else, but at this point I realized that the NaOH had precipitated all over the cup. I also noticed that the cup's bottom had turned mostly red. I assume this is rust.

So two questions: how do I get a NaOH solution at that temperature (by varying concentrations/processes or what), and what kind of container can I use (as it seems the stainless steel measuring cup was a bad idea; I considered glass but I'm afraid of ruining whatever glass container I use by coating the inside with sodium silicate)?
« Last Edit: September 05, 2007, 11:22:34 PM by BlueTheCow »

Offline limpet chicken

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Re: Obtaining a hot NaOH solution
« Reply #1 on: September 06, 2007, 08:23:21 AM »
It would be helpful to post more information on what you are trying to test, as we might be able to suggest more practical alternatives.

The boiling point of water at one atmosphere, is 100 degrees C, so without heating it in a sealed container, it couldn't be done easily without boiling off all the water, hermetically sealed rxn vessels are NOT reccomended though, as if it explodes on increase of pressure, you not only have container fragments going off in your face, but boiling NaOH, which from past experience, I can tell you, isn't really a pleasant experience ;)

One thing you could try, is microwave heating, as microwaves are able to superheat water, so long as the surface isn't disturbed, although I would do this *only* while wearing suitable face, eye and body protection, as well as thick gloves, and preferably, handling at some distance, as disturbing the surface even slightly, of such a superheated fluid, can cause it to suddenly flash up in a cloud of superheated steam.

You aren't trying to isolate sodium metal are you by any chance? if thats your aim, then dissolving NaOH in aqeous solution is pointless, as any Na formed will react instantly leaving you with yet more NaOH, and hydrogen gas, so for electrolysis experiments, the hydroxide must by fused by heat from a burner or blowtorch, and kept in the molten state

Oh, and I would try aqquiring a heatproof ceramic pot of some description, for handling hot or boiling NaOH, or fused NaOH melts, as they attack most metals, and to an extent, graphite crucibles and electrodes with great readiness.
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Offline Borek

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Re: Obtaining a hot NaOH solution
« Reply #2 on: September 06, 2007, 08:40:51 AM »
The boiling point of water at one atmosphere, is 100 degrees C

What about boling point elevation? We are talking about highly concentrated solution.
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Offline lutesium

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Re: Obtaining a hot NaOH solution
« Reply #3 on: December 22, 2007, 11:22:30 AM »
Yes I also do think the same way as Borek!!! But I don't think that the temp would hit that much 'cuz much of the NaOH will crystallyze out before these temp...

If you want Na metal you must electrolyze melted NaOH or the easiest and the cheapet way is to call your Chemical Supplier and to want a kilo!


Lutesium...

Offline Borek

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Re: Obtaining a hot NaOH solution
« Reply #4 on: December 22, 2007, 11:52:38 AM »
Yes I also do think the same way as Borek!!!

You do?

Quote
But I don't think that the temp would hit that much 'cuz much of the NaOH will crystallyze out before these temp...

You don't :)

Solubility rises with the temperature. I don't have NaOH data at hand, but for KOH solution made by mixing 500g KOH with 100g of water boils at 312 deg C. Exact number for NaOH will differ but the principle will be the same. 200 deg C seems possible to me.

Note that it is not easy to prepare such solution, as it will tend to dry out during heating.
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