Dr. Beaker - 13-9-2005 at 08:21
a conceptual question:
I knwo that desalination could be made by method called electrodialysis (
see scheme) but if, say, I take solution of acid and subject it to electric field (strong enough to overcome electrostatic atraction between the ions)
whould there be ph gradient in the solution (i.e H+ conc. falling in the area of the cathode and rising near anode)? what do you think?
Mr. Wizard - 13-9-2005 at 08:54
If you do that with a non conductor you end up with a capacitor. Energy will be stored by the material between the charged plates. To actually move
the ions away from each other would require a tremendous field gradient, or saying it another way, high voltage. The physical strength, and insulating
properties of the container and electrodes would fail if you actually separated say a mole of H+ and OH- The electric force is very strong. IMO you
would get some slight charge separation both in the electrolyte and in the container walls, but you couldn't develop a field strong enough to see
actual useful H+. Water actually has a very high dielectric constant. You might succeed in 'orienting' some molecules with the field, as
happens in piezoelectric crystals.
Quibbler - 13-9-2005 at 09:10
Quite right the field stength would have to be very large. If however you put in other ions at the right Cd2+ say using a cadmium electrode the H+
would move to the left (as H+ has a very high mobility)and the pH would be reduced. Enough to produce a colour change in a pH indicator.
thanx
Dr. Beaker - 13-9-2005 at 09:51
thanx for the insights. that what I thout more or less. this can have very nice implication for me 
12AX7 - 13-9-2005 at 13:20
Yeah, and as far as I know, that's exactly what you're doing when you electrolyze a solution. It consumes energy because 1. the solution is
conductive and acts as a circuit element, and 2. you are performing physical work by rearranging the ions. As a result, work is proportional to
charge.
Tim
Weird Thermodynamics
franklyn - 11-4-2007 at 01:56
Rather than sort, it seems it will entirely immobilize by freezing , given a strong enough electric field.
http://www.aip.org/pnu/2005/split/742-1.html
Loud resonant sound will refrigerate also
http://www.mecheng.adelaide.edu.au/anvc/thermoacoustics/inde...
.