Author Topic: Making Na  (Read 3330 times)

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acx01b

  • Guest
Making Na
« on: October 28, 2004, 03:08:00 AM »
NaOH has low melting point (324°C)

what about the electrolysis (with Pt electrodes)
of melted NaOH ?
is it easy (let's say 1A will give correct yields nearly 0.5mole per hour)

inert gaz is needed becose O2 reacts with melted Na formed...
what about using desoxygenated air (O2 --> CO2) for it ?

thanks for advices.

pyroflatus

  • Guest
is it easy It's difficult and inadvisable for...
« Reply #1 on: October 28, 2004, 10:38:00 AM »
is it easy
It's difficult and inadvisable for the home chemist.
Without knowing you but having read a few of your posts, I think you either wouldn't succeed, or would hurt yourself.

Perhaps stick to something more forgiving than sodium until you get up to speed.

And this post should be in the Newbee forum.
And are you legally an adult?

Lestat

  • Guest
Do not use Pt electrodes, too expensive and...
« Reply #2 on: October 28, 2004, 01:01:00 PM »
Do not use Pt electrodes, too expensive and very little point. Copper electrodes work very well, with barely any noticeable attack on the metal by NaOH.

The formed Na has a tendency to form little balls which spit and crack at the melting temperature.

The answer is, to use a knife and an old spoon to dig the Na out of the NaOH as soon as it is formed and transfer it to a jar full of hexane or naptha for storage.

Bee sure to use eye protection, and wear gloves.
A car battery is quite sufficient to provide the electricity.


acx01b

  • Guest
And are you legally an adult?
« Reply #3 on: November 01, 2004, 10:01:00 PM »
And are you legally an adult?
lol
 yes i am ty

i am gonna try with very low quantity (2-3 grams of NaOH) in a broken at the top flask, supplier of the flask says 500°C maximum so 350 should not be a problem

i know that if Na burns it will be dangerous so i am gonna wear what is needed (glasses, big clothes)

pyroflatus okey i am gonna hurt myself good for me i am stupid and i like try dangerous things...

the true is that my level in chemistry is not bad and i know that with very low quantities many reactions can be tried step by step without many danger.

last day i tried but i got f bad Amperage: like 0.05... with 15V

pyroflatus

  • Guest
Oh well, if you're determined to do it.
« Reply #4 on: November 02, 2004, 01:29:00 AM »
Oh well, if you're determined to do it. Good luck.
>last day i tried but i got f bad Amperage: like 0.05... with 15V

Sounds like you're using a 50mA rated power supply, or something with internal series resistance of 300 ohms. Molten NaOH should have quite low electrical resistance (but I couldn't find a figure quantifying this. Temptation may send me off to the 'lab' with multimeter in hand... but I did find that Downs cells that are used commercially to produce sodium from sodium chloride run several tens of thousands of amps of current.)

Like Lestat says, a car bettery would be your friend, as it'd supply a couple of hundred amps is need be.

Oh, and if you're already melting NaOH and have a multimeter, woudl you be so kind as to measure its resistance while molten?

Lestat

  • Guest
A car battery WILL do the trick, SWIM picks up
« Reply #5 on: November 02, 2004, 10:26:00 AM »
A car battery WILL do the trick, SWIM picks up partially discharged car batteries for free from the local waste dump and they DO work well, SWIM knows this from past experience.

Actual Na burning, as opposed to beeing dumped in water isn't that violent in SWIM's experience, although he doesn't waste large amounts on this, but small amounts just burn intensely without exploding, similar to magnesium or Li burning.


stratosphere

  • Guest
you should be able to look up the conductivity
« Reply #6 on: November 02, 2004, 01:01:00 PM »
you should be able to look up the conductivity of molten NaOH, or NaCl in something like the chemical/physics handbook, which most any medium sized public library will have.
keep in mind the total conductance (inverse of resistance) is proporational to the area of the electrodes, and inversley proportional to how far apart they are.

i belive in commercial operations the heat to keep the salt molten is supplied by resistive heating, which is not what im suggesting you should attempt as that wouldn't be well suited to lab operations, rather im just using that to show that the conductivity might not be all that huge.
the conductivity of brine for instance is many many factors of 10 less then that of metals, more on the order of the conductivity of undoped silicon.

why not keep the cell in an atmosphere of N2, Ar or He?
it should be that hard to do.
i wonder if the Na could be wicked off using a mettalic braid, like is done with solder to prevent the splattering?

acx01b

  • Guest
lestat said: Copper electrodes work very well,
« Reply #7 on: November 04, 2004, 03:39:00 AM »
lestat said: Copper electrodes work very well, with barely any noticeable attack on the metal by NaOH

and because i'm stupid i tried... even in water electrolysis Cu --> Cu2+ ....

the melted naoh solution became blue in 3sec with 17V 0.7A (i got a new DC generator)

could not look at the conductivity because some yellow sparks appeared in 3sec... i'have just put the power off, the gaz of, and run away the kitchen...lol
maybe the 2 electrodes were not spaced enough (0.5-1cm) i am gonna try with 2-3cm spacing

Graphite electrodes: do not use (carbone reacts)
Copper and all metals: do not use at the anode (Cu --> Cu2+)
Pt electrode: i have 3 platine electrodes: 8cm 3cm and 2.5cm... i hope it wont be destroyed but i am gonna try with the smaller one at the anode and copper at the cathode.

0.7A is cool

acx01b

  • Guest
lol i tried with Pt at the anode and Cu at the
« Reply #8 on: November 04, 2004, 05:26:00 AM »
lol

i tried with Pt at the anode and Cu at the cathode:
1st i melted the NaOH (~~5grams)
each time i started the electrolysis i didn't get
Cu --> Cu2+ but some Cu was leaving the electrode to go in the solution (orange-brown stuff floating on the solution, maybe in 2sec all the solution was brown)
then the brown became white and a little blue (much less than the 1st time) i wonder what reaction was happening at this moment (CuO --> Cu(OH)2 ?)

next try: 2 Pt electrodes

 by the way i measured the conductivity: 0.3A 17V between 2.3 and 3.3 MegaOhm (2.9 while electrolysis, 2.3 at this moment just after electrolysis is stoped) and 30sec after heating has been stoped, 3.3 Mohm.

Lestat

  • Guest
I did not notice any erosion of the electrodes
« Reply #9 on: November 04, 2004, 08:32:00 AM »
I did not notice any erosion of the electrodes or tainting of the NaOH when copper was used as the electrodes, the copper was old piping however, and perhaps an oxide layer had formed on the electrodes and served to protect from erosion.

Sorry :(


acx01b

  • Guest
ok this was the last try: these sparks at one...
« Reply #10 on: November 04, 2004, 10:17:00 AM »
ok this was the last try:
these sparks at one of the electrodes are really making me affraid (melted Na + O2 + spark --> omg i dont wanna know)

so i stop after 30x2sec electrolysis: note for who wanna try the solution became black but the electrodes have not reacted (the 2cm Pt electrodes still measure 2cm)

 i wonder what was the reaction between melted NaOH and copper... maybe i should try again with pure NaOH because this time i used the same blue NaOH that i got last try...

ho~~ho~~ho while washing the elecrodes i saw that one of the two was making bubbles with water.... 2Na + H2O --> Na2O + H2? what a yield i got something like 3.3mg of Na (cristallized with 5grams of NaOH)!

bio

  • Guest
Na Cell
« Reply #11 on: November 04, 2004, 11:58:00 AM »
This is from Ullmans. I was unable to copy the drawing. It shows a diaphragm between the electrodes of steel. Try 18/10 or 18/18 Stainless. A carbon anode should also work and is used in the Downs NaCl cell. The screen keeps the O2 bubbles from reaching the central cathode and the sodium floats to the top. The cathode is fed from below and the cylindrical anode and  screen project above the level of the cell. There is a duct in the annular space between the cathode and screen for the hydrogen.

............Using the same principle by which davy discovered sodium, castner developed a process for producing the metal on a large scale from molten sodium hydroxide in an electrolytic cell (Fig. (2)). This process was operated at Niagara Falls (United States) and Rheinfelden (Germany), and was the only practical method for sodium production from 1881 to the mid-1920s. Cheap hydroelectric power was available at both locations.
The Castner process yields sodium, hydrogen, and oxygen:
4 Na+ + 4 e– ¾® 4 Na (cathode)
4 OH– ¾® 2 H2O + O2 + 4 e– (anode)
2 H2O + 2 Na ¾® 2 NaOH + H2
The overall reaction is:
4 NaOH ¾® 2 Na + 2 NaOH + H2 + O2
Thus the current efficiency cannot exceed 50 %. In practice, current efficiencies of <45 % were achieved.

In the Castner cell (Fig. (2)) a cylindrical nickel anode surrounds the copper cathode concentrically. If NaOH is replaced by a molten salt containing NaCl, the collection and containment of the chlorine evolved cause problems, which are solved only when the positions of the anode and cathode are reversed, as in the Downs cell in which the anode is surrounded concentrically by the cathode.




The Castner process yields sodium, hydrogen, and oxygen:
4 Na+ + 4 e– ¾® 4 Na (cathode)
4 OH– ¾® 2 H2O + O2 + 4 e– (anode)
2 H2O + 2 Na ¾® 2 NaOH + H2
The overall reaction is:
4 NaOH ¾® 2 Na + 2 NaOH + H2 + O2
Thus the current efficiency cannot exceed 50 %. In practice, current efficiencies of <45 % were achieved.