idrbur
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complication in performing castner process?
I want to make sodium using castner process.
In this process sodium hydroxide is melted at 330 degree celcius and electrolised
But wikipedia states that if temprature goes above this temp. Than the produced sodium metal will dissolve in the solution and i does not have
anything to control the temp.
So,there is any way to recover sodium from solution or to prevent it from dissolving ?
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aga
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I am not certain, but i think the electrolysis causes heating, so you can control the final temperature by stopping/starting the electricity.
It needs external heating to get the NaOH molten to start with.
Molten NaOH is very nasty, so work Safely if you attempt this.
Edit:
Thought so. Heating is only required when melting the NaOH.
After that the electric current keeps the heat up.
https://www.youtube.com/watch?v=vtbUH99mTvc
[Edited on 15-7-2015 by aga]
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BromicAcid
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Dissolve really doesn't convey the reality of the situation:
Na + NaOH <----> Na<sub>2</sub>O + H<sub>2</sub>O
You overheat a Castner Cell and you end up with your electrolyte turning to trash. Reaction above starts to predominate for one reason or another and
instead of getting nice globules you end up just making more hydrogen and oxygen and less sodium. Yes the reaction is reversible but the water ends
up either evaporating from the temp or reacting with your sodium setting you back a step. At least that is my understanding. There is a temperature
range, a sweet spot, where you want to hold the reaction. Dollars to doughnuts it is outlined in the thread on Hot Electrochemical Sodium somewhere.
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aga
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Does the Conservation of Mass principle cease to apply for this process ?
No wonder i struggle with QM.
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Texium
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Quote: Originally posted by aga  |
Does the Conservation of Mass principle cease to apply for this process ?
No wonder i struggle with QM. |
Gah, I was going to balance it and be a smartass about it, but then I realized
that no matter what you do there's always an extra H or two.
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BromicAcid
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Marvin had an interesting post in the Hot Electrochemical Sodium thread from 2003 | Quote: | According to a book on the manufacture of sodium metal that Ive been quoting for several years now (paraphased),
Yeild of a castner cell drops from 80% at 5C above to 0 at 25C above the melting point because the solubility of sodium metal in the hydroxide becomes
so high the solution becomes a metaloid. This conducts electricity like a metal and electrolysis stops. |
Which is one of the theories that I had read. But I had also read that the sodium will react under higher temperature conditions. I have found a few
references in the thread but it likely reacts along the lines of this ACS paper:
2NaOH + 2Na ---> 2Na<sub>2</sub>O + H<sub>2</sub>
After brushing up in the sodium thread it seems more likely the metalloid issue props up when only slightly greater than target but the reaction issue
crops up with unregulated heating. Then again it's been a long time since I covered this material. The majority of my posts are from 2003-2004 
[Edited on 7/15/2015 by BromicAcid]
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idrbur
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Thanks to all of you for the reply.
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idrbur
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| Quote: |
Heating is only required when melting the NaOH.
After that the electric current keeps the heat up.
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Thus this also work for molten NaCl .
[Edited on 16-7-2015 by idrbur]
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