Sciencemadness Discussion Board

Sodium by electrolysis?

JCM83 - 18-4-2011 at 19:21

So I'm trying to make some sodium metal for my students. I used sodium chlorate because of its low melting point, applied the electrodes and ran a 40 volt current through it. Instead of getting sodium metal, I got some kind of... grey solid. It's brittle like a salt, definitely not metal.

The molten salt is white/transparent liquid. When I turn on the current I see... a lot of bubbling, the development of a metallic-grey liquid layer on top of the molten salt. More bubbles form, and then all of a sudden it fizzes up, and what is left behind is a red-hot glowing solid which quickly cools and forms a solid mass- looks like a magma mass cooling, or something- around the positive electrode.

So that's weird to begin with- the positive electrode, not the negative one. I expected sodium metal to gather around the electrode, but instead I get this nonmetal slag. What's going on? Why am I not getting the shiny white metal?

Bikemaster - 18-4-2011 at 20:46

I am not sure but I bet on the oxygen release from de decomposition of the chlorate is oxiding the sodium...

froot - 18-4-2011 at 22:43

Molten Sodium chlorate? *shiver*
Try sodium perchlorate dissolved in propylene carbonate, proceeds at RT and much smaller chance of a big bang.

Hades_Foundation - 18-4-2011 at 22:54

That can't work, can it? :o
(the sodium chlorate electrolysis I mean)

[Edited on 19-4-2011 by Hades_Foundation]

ScienceSquirrel - 19-4-2011 at 02:46

To be honest this sounds incredibly stupid.
Electrolysing a molten salt which is a strong oxidising agent to try and make a metal which reacts vigorously with oxidising agents :(

m1tanker78 - 19-4-2011 at 06:09

I also think your choice of salt is BAD but I have a couple of questions for you, JCM.

1. What material did you use for the electrodes?
2. What material and roughly what dimensions for the crucible?
3. Describe any smoke and odor(s) evolved throughout your experiment.
4. How are you trying to collect the sodium?

I've never electrolized molten chlorate (and I probably never would waste good chlorate that way). I'll almost bet it's decomposing both thermally and electrolytically, leaving you with NaCl, among other things.

If you're getting large bubbles at the anode (positive 'trode) that seem to rise and harden into a shell then I bet you're using carbon (graphite) for the anode. Hot Cl or O will erode graphite fairly quickly but it's cheap and plentiful so it's well worth it. But that parasitic Cl... I was glad to say goodbye to it! :o


symboom - 24-4-2011 at 06:24

a bit dangerous but sodium and potassium can be made easily from molten sodium hydroxide potassium can be made from that to but catches fire as soon as it is formed
potassium metall (potassium from potassium hydroxide you need argon if you want potassium)
(sodium does not combust as easily and can be made from sodium hydroxide)
sodium metal
videos of making sodium and one of making potassium
--hope this helps btw never do this in aluminum or zinc container they will dissolve in sodium hydroxide and potassium hydroxide must be iron

[Edited on 24-4-2011 by symboom]

woelen - 24-4-2011 at 09:23

Are you kidding us? Molten sodium CHLORATE for making sodium? You want to make sodium for your students in this way? You should know better.

Making sodium from a molten salt indeed can be done, although the required apparatus is not simple and one must be very careful to exclude air from the apparatus in which the molten metal is formed. A suitable choice of molten salt is NaOH, but this is very corrosive and splashes of the molten NaOH are extremely corrosive!

jsc - 24-4-2011 at 16:37

How to prepare metallic sodium:

By volume thoroughly mix and grind:

100 parts dessicated sodium carbonate
45 parts carbon black or activated carbon powder
25 parts dry, precipitated calcium carbonate

This mixture is packed into a fused silica (or stainless steel) tube and placed in an insulated environment, such as a furnace. A simple insulation can be made by molding a refractory cement around the tube leaving a channel for the burner gasses. The mold must be made slightly loose or it may crack the tube. You can make a channel by rolling beeswax into a cord then spiraling the cord around the tube. Then cast the refractory around it. When you bake the refractory to set it the wax will melt and a spiral channel will be left around the tube.

The burner should fire into an insulated firebox (also cast at the same time) which is below the tube and which exhausts into the channel.

One end of the tube is plugged (that is where you insert the raw material). The other end of the tube exits by a narrow passage into a condensation chamber. This chamber's size and shape is dictated by the size of your tube and the intensity of your fire. The chamber is maintained at a temperature determined by experience. Below the condensation chamber is a receiving flask containing annhydrous mineral oil. There is a 6" air drop from the condensation chamber to the receiving flask. The purpose of the air drop is to cool the hot sodium before it comes into contact with the oil.

Elemental sodium can also be produced by electrolysis of sodium hydroxide, but the technical complexity involved is much greater than the process described above.

[Edited on 25-4-2011 by jsc]

[Edited on 25-4-2011 by jsc]

Heinrich - 24-4-2011 at 23:24

Working with molten salts on a daily basis for several years, i would say that by carefully using an euctectic mixture of KCl and NaCl is a great way of producing Na. You would have to use an inert atmosphere gas such as Ar (5N) pre-dried with silica or something, as you need to get the chlorine gas out asap to prevent back reactions. The required temperature should be no higher than 600 C, though i do not remember the phase diagram by heart. You should do a quick CV sweep prior to electrolysis in order to identify the potential peaks for Na and K and do potentiostatic electrolysis near the Na peak. Use large cathodic surface area and if you don't care about back reactions, use a graphite crucible and employ it as anode. I guess this method has some demands for equipment, but if your institute has equipment for molten salts (which i guess since you used molten sodium chlorate (think HSE ffs!)) then it should be a quick and easy job.