OK Stable pure water will be difficult to maintain but what

[WayneL]

Hi

Ok, from the last threads on pure water I have established that

1/ Water's max resistance is apx 18.3MR
2/ Pure water does not stay pure for long, thus it acts as a great solvent.

For my experiment I need a stable ion water solution to measure atmospheric
effects on a particular system.
Thus at what mg/ltr of NaCl can I add to water to ensure relative stability
e.g. it will stay at a set conductivity for "fair" amount of time.
Forgive the fluffy term "fair" but I do not want to restrictive answers.

Cheers

Wayne

 

[Rich Grise]

On Wed, 05 Jan 2005 18:44:24 +0000, WayneL wrote:

Hi

Ok, from the last threads on pure water I have established that

1/ Water's max resistance is apx 18.3MR
2/ Pure water does not stay pure for long, thus it acts as a great solvent.

For my experiment I need a stable ion water solution to measure atmospheric
effects on a particular system.
Thus at what mg/ltr of NaCl can I add to water to ensure relative stability
e.g. it will stay at a set conductivity for "fair" amount of time.
Forgive the fluffy term "fair" but I do not want to restrictive answers.

If you just need a certain calibrated conductivity, use something like
H2SO4, not NaCl. The chlorine comes out of solution and causes a terrible
mess. A drop or two of H2SO4 makes really nice ions, and the sulfate just
sits there.

Good Luck!
Rich

 

[Robert Baer]

WayneL wrote:

Hi

Ok, from the last threads on pure water I have established that

1/ Water's max resistance is apx 18.3MR
2/ Pure water does not stay pure for long, thus it acts as a great solvent.

For my experiment I need a stable ion water solution to measure atmospheric
effects on a particular system.
Thus at what mg/ltr of NaCl can I add to water to ensure relative stability
e.g. it will stay at a set conductivity for "fair" amount of time.
Forgive the fluffy term "fair" but I do not want to restrictive answers.

Cheers

Wayne

*ADD* a contaminant?????????????????
(nuts)

 

[WayneL]

Hi Dieter

My latest work involves establishing my experimental parameter
space. Thus I need to remove the atmosphere and then re-introduce it one
gas/substance at a time. So flush out my chamber with argon and run my
tests contaminated with "pure water" (the combs with several with AC and
several with DC), then repeat with CO2 then N2 then O2 etc...
For the Dc I will use a galvanostat/potentiostat and for the AC I will use
an impedance spectrometer.
So you can see why I need the pure water as I am trying to simulate the
effect each of the atmospheric condition has on water. Water being the most
likely vehicle of contamination for electrical good (not forgetting beer
:-]).

On another thread there was a discussion on overpotential(s). If I have two
copper electrode and I need to find the overvoltage then won't they cancel
each other out or do they add up so Cu2+(aq) + 2e- -> Cu(s) = 0.34 so is it
2x0.34 or 0.34-0.34 (or have I lost the plot?).

Cheers

Wayne


"Dieter Britz" <britz@chem.au.dk> wrote in message
news:cris9b$lg9$1@news.net.uni-c.dk...

WayneL wrote:
Hi

Ok, from the last threads on pure water I have established that

1/ Water's max resistance is apx 18.3MR
2/ Pure water does not stay pure for long, thus it acts as a great
solvent.

For my experiment I need a stable ion water solution to measure
atmospheric effects on a particular system.
Thus at what mg/ltr of NaCl can I add to water to ensure relative
stability e.g. it will stay at a set conductivity for "fair" amount of
time.
Forgive the fluffy term "fair" but I do not want to restrictive answers.

Ah, now we are getting somewhere! All you want is a constant
conductivity. You need to think about just how constant you want
it (defluff!). Reasonably pure water might have a conductivity of
about (say) 1-10 Mohm cm or 0.1-1 microS/cm. If you are happy with
fluff at a level of 0.1%, you need to add enough electrolyte to make
a solution having 1-10 milliS/cm. You can look up tables of equivalent
conductance to work out the required concentration for a given
electrolyte. Since I presume you are not going to electrolyse this
solution (which would change the conductivity), NaCl is OK. KOH is
NOT; it would absorb CO2 from the air and the conductance would drift.

I see that I misspelled "quartz" in my previous posting. Very
embarrassing, so sorry.

--
Dieter Britz, Kemisk Institut, Aarhus Universitet, Danmark.

 

[Ted Edwards]

Mark Jones wrote:

Another great ion source is KOH - potassium hydroxide. It makes a
great electrolyte for disassociating large quantities of distilled
water. (Just supply a few amperes to some platinum electrodes...)

I'm under the impression that one of the mechanisms for deterioration of
vented cell NiCds is gradual absorption of atmospheric CO2 converting
the KOH to K2CO3 thus neccessitating periodic replacement of the
electrolyte.

Ted