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[Physltest] [Phys-L] Re: anomalies?



The 82nd edition (2001-2002) of the
_CRC_Handbook_of_Chemistry_and_Physics_ lists the reduction potential
for Li+ to Li as -3.0401 V (p. 8-23). It also lists the work function
for Ni as between 5.04 eV and 5.35 eV, depending on the surface
orientation, and the work function for Pt as between 5.12 eV and 5.93
eV, depending on the surface orientation, with a value of 5.64 eV for
polycrystalline Pt (p. 12-130).

Daniel Crowe
Oklahoma School of Science and Mathematics
Ardmore Regional Center
dcrowe@sotc.org

-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of Ludwik Kowalski
Sent: Wednesday, January 12, 2005 4:10 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: [PHYS-L] anomalies?

I am working with a simple DC cirquit. It is a power supply (internal
r=1.6 hms) with a voltmeter at its output. An electrolytic cell
(platinum anode and nickel cathode) is connected to the power supply,
through an ammeter. What can be more simple?

The current versus voltage relation is different from what one would
expect from a metallic resistor. First the current is ~zero (below ~10
microamps that I would notice), up to about 2.9 volts. Then the current
starts changing linearly at the rate of about 12.4 V/A, up to 650 mA at
11 volts. When the concentration of the electrolyte (Li2SO4 in water)
doubles (goes from 0.21 M to 0.42 M) the threshold remains 2.9 but the
slope of the line lbecomes 11 V/A.

I have three questions.

1) How to interpret the threshold of 2.9 volts? (I do not have a table
of electromotive potentials for different metals at home. Is 2.9 a
difference between Ni and Pt?)

<snip>
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