DirtyDan
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Na from NaCl by electral
Hey, im new and dont know if its a good idea to post a new topic but i couldnt find too much personal info on obtaining Na from salt. Theres a lot of
info on the new, but no actual pictures, or self experiences, just alot of stuff from the crapbook and alot of controversy on it. Many people,
including my chemistry teacher, said that heating NaCl to 800c and applying electrolysis would cause the Na to form but that it would oxidize in the
air quickly from the intense heat. I would have tried it by now, but im unsure of the best way to melt something at that temperature also. Ive seen
pictures of molten salt on a bunsen burner, but i dont want to try that until im sure of my power source so that i wont have to let it electrolize for
20+ hours..  Anybody have any personal insight or more info on how the reaction
goes?
Thanks in advance
Also i thought it may be better to ask a more specific question since my others may be common knowledge. What is the best amount to be run through the
molten NaCl? 12v 5a?
[Edited on 27-3-2004 by DirtyDan]
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BromicAcid
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Well, first off, there is a topic already up in the technochemistry section: Sodium! but that thread is getting a bit long. However this should probably have been posted to it. That aside, it is true that if you try to
electrolyze NaCl at these temperatures without protection from the atmosphere it will oxidize pretty much instantly. Also the chlorine coming up from
the anode will react back with the sodium on the surface if not properly separated.
It should be noted that industrially a 33% NaCl 67% CaCl2 mixture is used melting at 580C. Calcium impurities are minimal especially since calcium
will crystallize out of the molten Na. The two electrodes in this setup are separated by a steel gauze diaphragm. However even at this temperature
air oxidation will be enormous, even electrolysis of molten NaOH at a considerably lower temperature still has unacceptable losses in contact with
air.
You should be able to find many technical details by looking up the Downs Cell in google and most likely pictures of setups.
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DirtyDan
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Thanks bromide, im looking now for Downs Cell, and i stupidly overlooked searching 'Sodium' and instead searched Na, which mostly turned me
to synethesis of other compounds besides sodium itself.
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darkflame89
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I dunno whether this is correct... If I electrolyse a solution of NaOH, oxygen is produced at the anode and hydrogen at the cathode. Then, won't
sodium be left??!!! Correct me if i am wrong..
Ignis ubique latet, naturam amplectitur omnem.
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BromicAcid
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You'll just be doing the electrolysis of water, if carried on exhaustively you would just get rid of the water and be left with sodium hydroxide.
Toward the very end you might have some sort of paste that might behave violently but nothing worthwhile expecially since any Na formed would react
back with any water in the paste.
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t_Pyro
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Commercially, soium hydroxide is manufactured by the electrolysis of concentrated brine using a mercury layer as the cathode. The sodium amalgam thus
formed is treated with water to get pure sodium hydroxide. Instead of adding water to the sodium amalgam, isn't there a way to extract the sodium
from the amalgam?
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BromicAcid
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It usually takes a lot of mercury for this method to be efficient for the main reason that sodium forms a solid amalgam with mercury that only has 2%
or at maximum 3% sodium by this method. But yes, there is a way to separate them, you can distill off the mercury, however distilling mercury can be
quite hazardous to your health.
One interesting thing, somewhat related to this is one of Humphry Davy's methods for isolating potassium. He took a block of KOH and set it on a
sheet of metal, the block had a depression in the top middle. He waited for it to take moisture from the air till it had a sheen, then he took an
electrode and put it in the depression and completed the circuit through the metal plate that the block was sitting on. His cathode in the depression
started violent reactions and "..small gobules having a high metallic luster, and being precisely similar in visible character to quicksilver,
appeared, some of which burnt with explosion and bright flame, as soon as they were formed, and others remained, and were merely tarnished, and
finally covered with a white film on the surface.."
This comes to the relation to the current train of thought in N. M. Hopkins modification to the experiment. The conditions were the same with the
exception that the depression in the top of the block was filled with mercury. "During the electrolysis the sodium hydroxide is moistened from
time to time. After about an hour, the mercury becomes immobile owing to the amalgamation of sodium with the mercury. The two metals can be
separated by distilling off the mercury; sodium remains behind."
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t_Pyro
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I was under the impression that the amalgam was liquid, cause the diagram of the plant in my text book shows the amalgam being pumped out of the cell
into a separate chamber where it is brought into contact with water.
Well, I don't think distillation would be a good idea... In the Wurtz synthesis, can we use sodium amalgam instead of pure sodium?
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BromicAcid
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At lower percentages the amalgam would be liquid, in the cell that you speak of it is constantly pumped so it is not an issue of getting as much into
the amalgam as possible just constantly circulating the cathode liquid. I was just assuming that mercury would be in limited supply so you would want
to obtain a maximum concentration before commencing distillation. The amalgam can hold higher percentages but doing so requires production in a
different way.
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In the Wurtz synthesis, can we use sodium amalgam instead of pure sodium?
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I'm not familiar with the Wurtz synthesis in particular but usually the amalgam can be substituted for the pure metal in almost all instances.
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t_Pyro
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The Wurtz synthesis involves the reaction of an alkyl halide with sodium to "couple" the alkane, producing a symetrical alkane and NaX:
2R-X + 2Na -> R-R +2NaX
If this works with the amalgam, maybe I could directly react the amalgam from my (hypothetical) cell with the alkyl halide.
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