David AuBuchon wrote:
Some questions about electrolysis if people can comment:
1. Some say H+ ions are coming off of the anode. If so, where do
they come from? And in the case it comes from a water molecule, where
does the leftover OH- go?
The anode is positive, H+ is positive, so they repel. H+ will be
attracted to the cathode. Hydrogen is produced at the cathode. See
http://en.wikipedia.org/wiki/Electrolysis for complete description
2. During the initial stages, when silver cations are coming off the
anode, if they exceed solubility locally (before many anions have had
enough time to reach the anode), do these ions form metallic
particles?
yes.
If so, how is it that ions (mutually repulsive) can get
together like that?
When dissolved they are ions which repel. When the solubility limit is
reached they combine back with their O-- or OH- counterpart, and thus
have no charge. If the OH versions bump into each other then it forms a
silver particle, and water plus oxygen.
Is it really like a collision just overpowering
that resistance?
A collision from the browning movement.
3. They say particles have a zeta potential (which is the case of CS
is negative). I suppose particles are said to be "in suspension"? In
solution, there are many silver ions with positive charge. Are these
negatively charged particles and positively charged ions mutually
attracted? Or are things "in suspension" in a different universe than
things "in solution"?
Both the silver ions and particles have a positive charge, thus they
will repel each other. For the silver particle to combine with a
negative OH ion would require energy to split an ion off the particle,
and this energy is more than that gained by combining with the OH ion,
thus it is not energetically available.
4. At the cathode, one electron reacts with one water molecule to
form (H + OH-). Then the H becomes H2 and escapes, right?
The electron combines with the H+, producing monatomic hydrogen, which
then either reacts with the cathode metal producing a hydride, or with
another atom producing H2. The OH ends up at the anode, and evolves as
oxygen. That is 4OH -> 2H2O + O2
5. The gray colored sludge on the cathode is metallic silver plating
out, right?
Correct.
Why does so little silver appear to occupy so much
volume? Is the sludge full of air bubbles, making it look like a lot?
It is like feathers, and can be occupied by water or hydrogen gas.
6. When there is excess silver hydroxide, why does silverhydroxide
want to convert to silveroxide?
The chemistry of a solution of silver hydroxide causes it to switch back
and forth between the two forms until they are balanced. The balance
can be shifted by various things such as temperature and pH, but as far
as I know this have not been studied significantly.
Wouldn't it want to agglomerate into
particles?
Apparently some do over time. I am not sure why the process seems to
stop after a few days.
Or is it a combination of both? What chemically happens
to make silver hydroxide become silver oxide?
2AgOH <=> Ag2O + H2O
7. So ultimately, there is some metallic silver particles, silver
ions (as either silverhydroxide or silveroxide)
yes
and silver
"particles" of silver hydroxide or silver oxide?
Silver hydroxide will not form a particle, it immediately converts to
silver oxide upon dehydration. Any silver oxide particles will
precipitate out, that happens if you exceed the solubility limit at that
temperature for it.
And I suppose there
are "inter-racial" particles, right? Like a particle that could have
some metallic silver, silverhydroxide, as well as silveroxide? Are
there actually any silver ions left just by themselves?
There are silver ions by themselves, that can be verified by measuring
the conductivity of the EIS. I don't think under normal conditions
there are any "hybrid" particles of silver with silver oxide/hydroxide
mixed in. However I do believe they can be produced, and experimental
evidence seems to support that supposition. If you take EIS and
evaporate water from it with heat, it will not precipitate, but can
actually approach or exceed 500 ppm. The solution becomes quite brown,
but it does stay in suspension. Upon diluting with water it will revert
back to normal EIS. This I believe is an indication of silver particles
being "glued" together by silver oxide particles, which form something
akin to a popcorn ball. Upon adding water the silver oxide dissolves
back into solution, and the particles separate again.
8. I think Marshall said the black char on the anode is silveroxide.
Was it originally silverhyroxide that turned to silveroxide?
I believe it is silver Oxide both from the oxygen reacting with the
silver, plus any silver hydroxide formed converting to oxide. Silver
hydroxide cannot be formed in the solid state (dehydrated or
precipitated) from what I have read.
Marshall
Thanks,
~David
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