Sciencemadness Discussion Board

Shiny sodium

nezza - 5-7-2012 at 13:19

I have recently acquired some sodium. The metal was originally coated with oxide so I have cut that off and resuspended the metal in boiled and cooled paraffin oil under argon. there was an initial slight reaction (expected) and some bubbles of presumably hydrogen released. The metal now shows a shiny surface. Is this a very thin oxide coating or what and have others experienced the same ?. I have attached a picture of the sodium.

Sodium.jpg - 139kB

Zan Divine - 5-7-2012 at 17:04

Metallic sodium is shiny, and hydroxide & oxides are not. If shiny, it's metal. So far, so good.

Enter....the diffusion leak. A diffusion leak is a leak driven not by pressure per se but by concentration. As long as the oxygen concentration in the bottle (moisture too, for that matter) differs from that outside, a driving force exists trying to equalize that. Inside the bottle, oxygen and moisture are consumed. The cap allows more oxygen and moisture to diffuse inward along the seal and this process never stops. Your surfaces will not be shiny by the time fall rolls around.

MrTechGuy1995 - 5-7-2012 at 20:10

Wait a sec, that looks a bit like potassium rather than sodium.
It's just a hunch though.

Zan is right.
If you want to keep them nice and shiny, put them in ampules.

chemrox - 5-7-2012 at 20:14

What about casting them in solid parafin? The pressure inside the casting would be negligibly low if done right. There are some liquid plastics one might use as well; tool-dip?? The latter case might be compromised by high vapor pressure of solvents... don't know much about the stuff.

Endimion17 - 6-7-2012 at 02:45

Do not remove the hydrogencarbonate coating. Although not as good as aluminium's oxide coating which stops the oxidation, this coating slows it down considerably. If you remove it, a new one will be built, and then you keep removing it and essentially wasting your sodium.

If you want sodium for display, you'll need to seal it in an ampoule. If you want a reagent, you don't have to bother with its looks. Simply cut the required amount each time you need it, and store the waste cuttings into a special bottle. After few years, when it's full, you can recycle the waste with a considerable yield.

BTW that seems like a rather small bottle. If those pieces are smaller than half of an AA battery, you should melt them into a solid piece and put that piece in a larger bottle filled almost to the top with boiled paraffin/kerosene/whatever.

[Edited on 6-7-2012 by Endimion17]