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| Marvin... |
 Posted: Wed Aug 19, 2009 9:45 am |
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erschroedinger at (no spam) gmail.com wrote:
[quote:df74fd2afe]On Aug 16, 11:52 pm, sorin <sorincosof... at (no spam) yahoo.com> wrote:
Concentration cells and absurdities of modern
science
A critique analysis of concentration cell and electrode phenomena is
provided at following link:http://www.elkadot.com/chemistry/Concentration%20cell%20and%20the%20s...
In the frame of actual physical chemistry it is found that
concentration cell works without a coherent explanation. Further, the
actual explanation can be proved to be false using simple chemical
reactions able to be performed in any low level school laboratory..
A new experiment able to clarify some of electrode phenomena is
proposed.
Regards,
Sorin Cosofret
Concentration cells work for the same reason all voltaic cells work --
one cell has a greater tendency to undergo reduction than another, as
a way of reaching equilibrium. Everything in nature strives to go to
equilibrium. When a Cu/Zn cell is running, the Cu(II) ions have a
much greater reduction potential than the Zn(II) ions, so it's out of
equilibrium. By reducing the Cu(II) ions (and lowering their conc.)
and oxidizing Zn to Zn(II) (and increasing their conc.), the cell can
move towards equilibrium.
The same is true for a conc. cell -- the side with a higher ion conc
has a greater reduction potential.
I tell my students to imagine it's a tug of war for electrons. With
Cu/Zn, each Cu(II) ion is stronger than each Zn(II) ion, so the Cu
half-cell wins the tug of war, pulling electrons to its half-cell.
But that reduces the Cu(II) conc, so it's like people dropping off the
stronger side of the rope. Eventually there are so many fewer people
on that stronger side that, while each one is still stronger than each
one on the weaker side, the two sides have equal pull and no electrons
move -- equilibrium.
The same is true for a conc cell -- each ion has equal pull, but one
side has more people on the rope than the other, so electrons are
pulled to that side. But they drop off until the 2 sides have equal
people pulling -- equilibrium.
BTW, there is no reaction in a conc cell between Cu(II) and chloride
-- it's simply a balancing of charge. Review your ionic and net ionic
rxns.
[/quote:df74fd2afe]
Agreed, but the important parameter is activity, not
concentration per se. The document equates concentration to
activity: "It is accepted that an equilibration of activity
(concentration) of sulfate ion represent ,,the engine” of a
concentration cell." |
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