adam7878
Harmless
Posts: 2
Registered: 3-10-2012
Member Is Offline
Mood: No Mood
|
|
Copper sulfate electrolysis with tungsten anode
Hi all,
I'm attempting to make sulfuric acid by electrolysing a solution of copper sulfate. I'm not using a graphite anode as they tend to degrade and fill
the solution with carbon particles. Instead, I tried tungsten welding electrodes because I read that tungsten was resistant to sulfuric acid.
For some reason, no current flows at all in my cell. However, if I replace the anode by a paperclip (presumably made of iron), current flows, gas is
liberated at the paperclip and copper is deposited on the other electrode.
I'm using the tungsten rods for both my electrodes.
Can anyone explain why this doesnt work with the tungsten anode?
Thanks
|
|
|
hissingnoise
International Hazard
Posts: 3940
Registered: 26-12-2002
Member Is Offline
Mood: Pulverulescent!
|
|
I can only assume that the oxide which formed on the anode is, at best, poorly conductive.
A platinum anode or platinum coated anode is called for . . .
|
|
|
LanthanumK
Hazard to Others
Posts: 298
Registered: 20-5-2011
Location: New Jersey
Member Is Offline
Mood: No Mood
|
|
I remember trying to oxidize tungsten using electrolysis and after an initial current spike the current dropped off completely and the electrolysis
stopped. Titanium has a similar problem, but the oxide coating forms an iridescent surface enabling it to be visible to the human eye.
hibernating...
|
|
|
hissingnoise
International Hazard
Posts: 3940
Registered: 26-12-2002
Member Is Offline
Mood: Pulverulescent!
|
|
| Quote: | | I'm not using a graphite anode as they tend to degrade and fill the solution with carbon particles. |
If you keep current density and electrolyte temperature low to minimise fragmentation and oxidation of the graphite you can get a dilute acid which
can be concentrated by boiling off the water.
Let the cell run for a few minutes after the colour has gone from the sol. and remove the now heavy copper-coated cathode before switch-off.
The produced H<sub>2</sub>SO<sub>4</sub> sol. when carefully filtered can then be concentrated to ~98% by heating . . .
|
|
|
adam7878
Harmless
Posts: 2
Registered: 3-10-2012
Member Is Offline
Mood: No Mood
|
|
Thanks a lot for the explanations.
What would be a good current density, approximately?
|
|
|
hissingnoise
International Hazard
Posts: 3940
Registered: 26-12-2002
Member Is Offline
Mood: Pulverulescent!
|
|
That depends on cell volume but whatever current plates out copper without affecting cell temperature . . .
Using a graphite cathode will ensure that no further metal ions are added to sol..
If your PSU isn't switchable then experimenting with various cell sizes will have to suffice!
|
|
|
tetrahedron
Hazard to Others
Posts: 210
Registered: 28-9-2012
Member Is Offline
Mood: No Mood
|
|
how about a PbO2 anode from a car battery? it's supposed to withstand H2SO4 and not decompose the acid
[Edited on 3-10-2012 by tetrahedron]
|
|
|
K12Chemistry
Hazard to Self
Posts: 63
Registered: 3-1-2013
Member Is Offline
Mood: No Mood
|
|
lead dioxide works almost as good as platinum
|
|
|
Fantasma4500
International Hazard
Posts: 1681
Registered: 12-12-2012
Location: Dysrope (aka europe)
Member Is Offline
Mood: dangerously practical
|
|
PbO2 anode would work, also you could perhaps use wolfram anode and lead cathode
perhaps what happens is that when using wolfram (tungsten, W) anode and cathode, it wouldnt work, dont hang me up on this, but i was explained that
copper - copper electrolysis of CuCl2 wouldnt work as they are just trying to coat each other..
lead is easy to get, your problem would just be to get some piece thats not wider than long.. you could perhaps just melt some into a simple gypsum
form
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
