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Forum index » Science and Technology » Chem » Electrochem
Help ! (about Nernst equation)
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Mike Amling
science forum Guru


Joined: 05 May 2005
Posts: 525

PostPosted: Thu Oct 06, 2005 1:54 am    Post subject: Re: Effect of pH Reply with quote

Quote:
Effect of pH

Click the Mechanism menu to open a Mechanism window, tick the "pH effect"
checkbox, change the number of H+ in the charge reaction, and then click
the
OK button to close the Mechanism window. Click the Kinetics menu to open a
Kinetics window, change the pH value in the Solution section, and then
click
the OK button to close the window. Run the simulation. You should see the
peaks shift when pH is larger or less than 7. As the pH value increases,
the
peak shifts to more negative potential. For a charge reaction

a A + h H+ + ne = b B

where a is the reactant number, b is the product numbers, h is the number
of
H+, and n is the electron number. The relationship of the peak position
with
the pH value usually is linear:

Ep = k1 - k2 pH

Where k1 and k2 are constants. k2 depends on the electron number, the
number
of H+, the numbers of reactant and product, and temperature. For a=b, it
becomes

Ep = k1- RTh/nF pH

For a=b and h=n, it becomes

Ep = k1- 0.059 pH

It shows that both peaks in CV shift to 59 mV more negative potential per
pH. These agree with the theoretical equation (2.5).



www.electrochemist.com
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Don Kelly
science forum Guru Wannabe


Joined: 30 Apr 2005
Posts: 166

PostPosted: Sun Dec 11, 2005 2:49 am    Post subject: Re: Building a Voltaic pile Reply with quote

----------------------------
<cornytheclown@hotmail.com> wrote in message
news:1134268135.405323.40630@g49g2000cwa.googlegroups.com...
Quote:
try some pennies and get some galvanized sheet metal...any heating and
cooling outfit can cut you some little squares of sheetmetal. might
even have some copper sheet laying around...or you could get some
copper pipe and cut it down the middle...spread and beat out flat with
hammer and cut some squares.....or you could get some galvanized
washers at the hardware store....
hardware store alsom might have small piece of galvanized metal
strapping they could let you have.

try lemon juice as an acid.....and maybe do some research on sal
ammoniac....I think thats what people used years ago to make homemade
cells......


Put the lemon juice on blotting paper between the pennies and galvanised
washers. This keeps the electrolyte where it belongs.
Alternatively stick a copper wire and a galvanised nail into a lemon.

--

Don Kelly @shawcross.ca
remove the X to answer
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samwyse@gmail.com
science forum beginner


Joined: 10 Dec 2005
Posts: 6

PostPosted: Sun Dec 11, 2005 3:26 am    Post subject: Re: Building a Voltaic pile Reply with quote

Many thanks to everyone who replied!

Dave wrote:
Quote:
the battery tester is probably meant to read current to tell you how good
the battery is.

Here's the incredibly cheap tester I used: http://tinyurl.com/8djef
-or-
http://www.radioshack.com/product/index.jsp?productId=2103165&cp=2032058.2032235.2032306&parentPage=family

Quote:
also, get rid of the salt, you want acid like vinegar or lemon juice or
dissolved vitamin c tablets. and remember, the towels need to be very wet
so the metals have a good path to drive ions through liquid... but they
shouldn't be so wet that the acid bridges between cells or it essentially
just shorts them out. a better material for the dividers is blotting paper,
but the towels will work if you get them wet enough.

That may be my problem, then. I worried about the foil shorting things
out, but not the paper. Those 1" squares flopped everywhere.

Quote:
just as a quick sanity check, with apple cider vinegar, one penny, and one
square of foil I get .7v at about 2ma. that won't be enough to budge a
battery meter but it registers well on a volt meter.

As an ex-EE, I'm ashamed to say that I haven't seen my voltmeter in
ages. I guess I need to go buy a new one.

Quote:
and remember, the
current is limited by the diameter of the penny and foil, stacking more in
series won't increase the current it can generate only the voltage. you
need more surface area to get more current. or hook them in parallel.

We're working off of a project in a book which claimed that twelve
cells in series would create a visible spark. Oh, well.
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Oscar Lanzi III
science forum Guru Wannabe


Joined: 30 Apr 2005
Posts: 176

PostPosted: Sun Jan 15, 2006 12:05 pm    Post subject: Re: Does this process seem feasible? Reply with quote

I don't see anything wrong with it. Don't e scared by the "alternating
current." The cathodic reaction may not be the reverse of the anodic
one.

--OL
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jpsmith123@yahoo.com
science forum beginner


Joined: 29 Dec 2005
Posts: 11

PostPosted: Mon Jan 16, 2006 12:13 am    Post subject: Re: Does this process seem feasible? Reply with quote

Thanks for your reply. In fact the alternating current was one of my
concerns. Intuitively, it seems that whatever may deposit on the
electrodes would be oxidized on the positive half cycle and reduced on
the negative half cycle, for a net effect of zero.

Regards,
Joe

Oscar Lanzi III wrote:
Quote:
I don't see anything wrong with it. Don't e scared by the "alternating
current." The cathodic reaction may not be the reverse of the anodic
one.

--OL
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Evgenij Barsukov
science forum Guru Wannabe


Joined: 09 May 2005
Posts: 137

PostPosted: Wed Mar 08, 2006 4:21 pm    Post subject: Re: RF...? Reply with quote

Peter_Hunnt@yahoo.com wrote:
Quote:
Hello
I don't know what is the best way to ask this, so I'm going to say it
in my plane language.
Is it possible to change the structure of chemicals with radio
frequency..?

That is a controversial topic, it depends how you define "chemicals".

What is clear is this:
- you can not break chemical bonds by RF (not enough energy)
- RF can heat up materials, which eventually can break weaker hydrogen
bonds (but this is not specific to RF, any heating can do that).

One caveat:
- heating is specific (higher or lower) depending on a nano-scale size
composition (more electrically conductive will heat up more). For
example one nano-scale aggregate (say a chromosome) can be heated more
than other (say membrane, or ribosome). This way temperature gradients
on nano-scale can be created.

This can (but have never been proven to) have effect on living
organisms, as temperature gradients _inside_ a cell can cause
some unusual concentration gradients disrupting usual processes.

Same way on larger scale, temperature gradients between tissues
(for example between nerves and fat or muscle tissues) could
cause unusual sensations and might again cause unusual processes
if strong enough.
Note that temperature gradients are already present in the organism
but they are generally in the direction from cooler (skin) to heater
(muscles).

To summarize - effect on chemicals is well understood,
while effect on continuously dynamically changing nano-scale composites
such as life objects is more subtle and still open for discussion. It
might well be that at some level RF will cause enough temperature
gradients to disrupt some processes.

Regards,
Evgenij
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Peter_Hunnt@yahoo.com
science forum beginner


Joined: 07 Mar 2006
Posts: 6

PostPosted: Wed Mar 08, 2006 7:13 pm    Post subject: Re: RF...? Reply with quote

What I'm trying to fing out is... Is it possible to get some compound
or chemicals. Alter their structure so that the chemical or compound
will be only affective when someone sends a RF wave. I don't know if I
can say it this way ..but polarize, make it only react when the
specific RF is send.
Lets say a chemical that normally when put in a sea water turns the
water red. Now is it possible to somehow alter the chemical that when
put in the water will not turn the water red but only when you transmit
a specific radio frequency wave will turn the water red?

peter_hunnt@yahoo.com
Thank you
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Lasse Murtomäki
science forum beginner


Joined: 17 Jun 2005
Posts: 35

PostPosted: Wed Apr 26, 2006 12:42 pm    Post subject: Re: graphite Reply with quote

Yes, it probably was off-scale.

--
Lasse Murtomäki
Helsinki Univ. Tech.
Lab.Phys.Chem.Electrochem.
lasse.murtomaki@tkk.fi
"Dieter Britz" <britz@chem.au.dk> wrote in message
news:e2nlm3$vue$1@news.net.uni-c.dk...
Quote:
Lasse Murtomki wrote:

Is there any value for the relative permittivity of graphite. It sure is
a
good conductor, but is the value infinite? I am testing a material
probing
kit and got an infinitely high value for a graphite disk.

Doesn't that just mean, it's off-scale? To be expected, I
guess, for a conductor.
--
Dieter Britz, Kemisk Institut, Aarhus Universitet
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