Post Tagged with: "electroneutrality"

Electroneutrality is dead?

pollack
Gerald Pollack

That is the highly controversial claim made by Kate Ovchinnikova and Gerald Pollack in Langmuir earlier this year.[Langmuir] Electroneutrality is a guiding principal in electrochemistry and is a method to understanding electrolytic cells (Pt electrodes in dilute aqueous NaCl solutions). It stipulates that any charge imbalance across an electrochemical system is quickly (~ns) balanced by the salt present in the water being driven by the electric field in such a way to neutralize that charge imbalance. Thus the need for salt bridges and all that wonderful G-chem stuff we have learned. There is even a cool little applet you can play with electroneutrality by the Harvey Project. When I tried to sit down with electrochemists to discuss the claims by O&P they quickly dismissed them out of hand after reading the beginning of their paper. So the big question is, did O&P stumble across something amazing or did they spectacularly overstate the results of their experiment.

I can summarize their paper succinctly:

electrochem setup
  1. Insert electrodes into electrolytic cell
  2. Turn on power supply
  3. Disconnect the electrodes from the circuit
  4. Remove the bridge between beakers
  5. Reconnect electrodes to measure residual charge in the two beakers.

The design seems thoughtful enough, but before I get into the merits of their results I need to take time to mention a few gems in their paper. Here is a quote from them.

Bubble formation occurred in all experiments (n > 20), although position and growth rate were inconsistent. In most cases, formation began during the charging phase and continued through discharge. Characteristics of bubble formation were not pursued in any detail, but may warrant future study.

But it doesn’t warrant further study,  all chemists know where their bubbles came from.

$$ \text{Cathode: } \text{H}_2\text{O} + 2\text{e}^- \rightarrow 2\text{HO}^- + \text{H}_2$$

$$ \text{Anode: } \text{H}_2\text{O} \rightarrow 2\text{H}^+ + \frac{1}{2} \text{O}_2 + 2\text{e}^-$$

usb-6009

An other eye catcher is that they didn’t use a standard electrochemical setup. They used my trusty NI USB-6009, I know that product well as a chunk of my thesis was acquired with it. It doesn’t make the experiment invalid, but why use crap when you are trying to disprove such a time honored concept as electroneutrality. Maz and I know from experience that the USB-6009 floats if their isn’t a sufficient load on it or if their isn’t an appreciable external voltage.

Here is a quote from them contemplating that HCl solutions have an overall positive charge.

One might speculate, for example, whether ordinary acidic solutions, which have low pH, might contain net positive charge, while ordinary basic solutions might contain net negative charge.

So far everything has been “quirky”, it isn’t until the end when you perceive something really odd.

Water appears able to adopt two structural networks that have mirror symmetry to one another. The fact that these networks are macro phenomena deserves further study.

A second and related issue is the potential for disturbance of these structural networks. It is now established that when water is left standing for long periods, it develops thixotropic properties, implying macrostructure.7 Such macrostructure is expected to be fragile. The fact that removing and inserting electrodes did not apparently ruin the charge-containing structure implies that, once formed, the structural network can re-form rather readily. This is an additional subject requiring further study.

7:Vybiral, B. Water and the Cell; Pollack, G. H., Cameron, I., Wheatley, D., Eds.; Springer: New York, 2006; pp 299-314.

It is with that last statement you say to yourself, “Oh, I get it. This is a homeopathy paper.” Water being able to adopt structures of the solutes that were dissolved in it is a hallmark of the quackery that is homeopathy. O&P’s claim isn’t that bold, but it has hints of the same idea. Claiming macrostructures (~mm) of water that extend past the picosecond domain is absurd.

Although I haven’t discussed the results of their paper, would you really trust it anyways?

Horacio Corti and Agustin Colussi have done an excellent job dissecting the technical irregularities of the paper and I encourage you to read their comments on the article (link below). If you come to a different conclusion or find me in error, please leave a comment and join the discussion.

Links

Mitch

By September 3, 2009 4 comments opinion, physical chemistry