Upsilon
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Alternate method for isolating sodium metal?
Most methods for isolating sodium metal I see are by electrolyzing molten sodium hydroxide. But why sodium hydroxide and not some other sodium salt
with a lower melting point? Take sodium bisulfate, for example. At such a low temperature, you could melt the salt under mineral oil without the
mineral oil even getting close to boiling. That way the sodium metal generated could go without ever being exposed to air. Similar things could be
done for other reactive metals as well, simply finding a low-melting salt containing the metal and melting it under mineral oil.
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gdflp
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Sodium hydroxide is used because it is one of the lowest melting, non-acidic, sodium salts. Electrolysis of molten sodium bisulfate wouldn't yield
any sodium metal because the anhydrous material doesn't melt at 59°C, the monohydrate does. Thus, any metal formed would instantly react with the
water to form sodium hydroxide. Anhydrous sodium bisulfate doesn't melt, rather it decomposes to sodium pyrosulfate at around 315°C. Sodium metal
would also likely react with any molten sodium salt that had an acidic anion.
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Upsilon
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The only salt I can find then that doesn't exist as a hydrate and has a reasonably low melting point is sodium thiocyanate. But I'm guessing the
thiocyanate anion will be too acidic as well?
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deltaH
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I think you might just have a 'surprise' form on the anode with sodium thiocyanate.
The beauty of sodium hydroxide is its low cost, low m.p. and availability. If you want a lower melting point, then you can use a eutectic of sodium
and potassium hydroxide, already mentioned elsewhere on SM, though you'd probably form a liquid 'NaK'.
[Edited on 21-9-2015 by deltaH]
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Upsilon
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I know that dangerous products can evolve on the anode, so I would keep the electrodes in separate vessels connected with a salt bridge. I would also
make sure that the system is well-ventilated.
I suggested thiocyanate because its melting point is below the boiling point of parrafin oil, in hopes to keep the metal from ever being exposed to
air. I have also found that sodium chlorate has quite a low melting point as well.
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annaandherdad
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I would't melt sodium chlorate with paraffin oil.
Any other SF Bay chemists?
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