Re: CS>basic dumb question
From: Marshall Dudley
Date: Fri, 28 Jan 2005 10:08:31
http://escribe.com/health/thesilverlist/m77263.html
> Here is a reference that shows the solubility of AgOH to be more
> than 100 ppm if the ph is less than 9!
> How the heck do you get known good information when the "experts"
> don't seem to be able to agree?
> Marshall
Silver hydroxide is insoluble in dw.
Take two 12 ga electrodes spaced 0.050 inches apart. Fill a glass
with dw to a wetted length of 4 inches. Apply 670uA/sq.in. current.
Here are the observations.
Fri Mar 25, 2005, 05:30:21 am
Setup Parameters
~~~~~~~~~~~~~~~~
volume : 300ml
initial conductivity : 1.1uS
wetted length : 4.63 inches
constant current src : 775.0 uA
Observations
~~~~~~~~~~~~
Time/Date Cell Voltage
Fri Mar 25, 2005, 05:41:11 am 4.0V
Fri Mar 25, 2005, 05:42:00 am 2.4V
Fri Mar 25, 2005, 05:44:58 am 2.5V <- cathode is black
Fri Mar 25, 2005, 05:48:00 am 2.5V <- anode starting to get black
Terminated the run.
Dw final conductivity is 1.0uS
The side of the cathode facing the anode is coated black. The
material is very soft and easily wiped from electrode. A shiny spot
appeared on the tissue after rubbing the electrodes. Examination
under a stereo zoom microscope showed a patch of black powder
embedded in the tissue. The central portion was shiny. Several other
shiny areas were apparent under the microscope.
During the short run, no Tyndall effect was visible in the dw in a
dark room. It was not possible to check for Tyndall between the
electrodes since they were spaced so closely that the laser beam hit
one or the other and the brilliant reflection made it impossible to
see anything.
The tissue was placed in a 3oz glass and covered with H2O2. The
black areas disappeared in a few minutes.
The test took 410 seconds. Silver hydroxide appeared on the cathode
at 226 seconds. The amount of silver liberated from the anode in
this time was 0.655ppm, but not all of it was involved in the
production of silver hydoxide (See calculations at the end.)
Conclusions
~~~~~~~~~~~
Silver ions released from the anode quickly reached the nearby
cathode.
Silver hydroxide formed in the Nernst Diffusion layer next to the
cathode:
Ag(+) + OH(-) --> AgOH
Some of the particles stuck to the cathode and formed a visible
black layer.
Pressure during rubbing decomposed the hydroxide to silver metal.
H2O2 dissolved the hydroxide and silver metal back to ions.
The solubility of silver hydroxide is less than 0.655ppm and
probably can be taken as zero.
--------------------------------------------------------------------
Calculations
Unit Conversions
~~~~~~~~~~~~~~~~
Coulombs = I * Seconds ; total number of Coulombs
CoulombsGram = 107.868 / 96485 ; Coulombs per gram of silver
ElectronsSec = I / 1.60217733e-19 ; electrons per second
Grams = CoulombsGram * I * Seconds ; Faraday's equation
Hours = Seconds / 3600
IonsPerNano = IonsSqInSec / 6.45e14 ; ions per square nanometer/sec
IonsSqInSec = ElectronsSec / SquareIn ; ions per sq. in. per sec
Litres = 3.785 * Gallon ; convert gallons to litres
Litres = Millilitres / 1000 ; convert millilitres to litres
Milligrams = Grams * 1000 ; convert grams to milligrams
Millilitres = 29.57 * Ounces ; convert ounce to milliliters
Minutes = Seconds / 60 ; minutes
NumberIons = ElectronsSec * Seconds ; number of silver ions
SquareIn = 0.25 * Length ; convert length to SquareIn
uASqIn = 1e6 * I / SquareIn ; current density in uA per sq in
uS = Milligrams / Litres ; 1 uS is 1 milligram per litre
uSPerHr = uS / Hours ; uS per hour
Input Parameters
~~~~~~~~~~~~~~~~
Hours = .063
I = 775e-6
Length = 4.63
Millilitres = 300
Solution
~~~~~~~~
Coulombs = 0.175
Grams = 0.000
Hours = 0.063
Litres = 0.300
Milligrams = 0.196
Millilitres = 300.0
Minutes = 3.780
Ounces = 10.14
Seconds = 226.8
SquareIn = 1.157
uASqIn = 669.5
uS = 0.655
uSPerHr = 10.39
----------------------------------------------------------------------
Mike Monett
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