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Marshall Dudley
Posted: Wed Dec 22, 2004 10:19 am
 
Silver chloride has a solubility of about .89 ppm in cold water.
Accoding to Le Chatelier's Principle the solubility will decrease in the
presence of additional chloride ions. So the addition of HCl or NaCl
will cause the solubility to drop.

However at an excess of chloride of ions a dichloroargentate complex is
formed, which is highly soluble.

Does anyone know at what point the solubility turns around and starts
increasing again with respect to the concentration of Cl ions, or the pH
of HCl?

I found one reference (
http://www.sampleprep.duq.edu/dir/Chapter2/Chapter2.htm ) that indicates
that this occurs around a molar concentration of 3, but that seems
awfully high (pH of -.48?).

Thanks,

Marshall
 
Farooq
Posted: Wed Dec 22, 2004 10:39 am
 
Marshall Dudley wrote:
[quote:1615c6ff12]Silver chloride has a solubility of about .89 ppm in cold water.
Accoding to Le Chatelier's Principle the solubility will decrease in
the
presence of additional chloride ions. So the addition of HCl or NaCl
will cause the solubility to drop.

However at an excess of chloride of ions a dichloroargentate complex
is
formed, which is highly soluble.

Does anyone know at what point the solubility turns around and starts
increasing again with respect to the concentration of Cl ions, or the
pH
of HCl?

I found one reference (
http://www.sampleprep.duq.edu/dir/Chapter2/Chapter2.htm ) that
indicates
that this occurs around a molar concentration of 3, but that seems
awfully high (pH of -.48?).

[/quote:1615c6ff12]
The website mentions 3M Cl(-) ion not the hydrogen ion concentration.
Did you mean pCl of -0.48? (pH is defined to be a positive number from
0 to 14; I don't think negative pH is of any use except as negative log
of a number greater than 1)
 
Marshall Dudley
Posted: Wed Dec 22, 2004 11:02 am
 
farooq_w@hotmail.com wrote:

[quote:af65976a3e]Marshall Dudley wrote:
Silver chloride has a solubility of about .89 ppm in cold water.
Accoding to Le Chatelier's Principle the solubility will decrease in
the
presence of additional chloride ions. So the addition of HCl or NaCl
will cause the solubility to drop.

However at an excess of chloride of ions a dichloroargentate complex
is
formed, which is highly soluble.

Does anyone know at what point the solubility turns around and starts
increasing again with respect to the concentration of Cl ions, or the
pH
of HCl?

I found one reference (
http://www.sampleprep.duq.edu/dir/Chapter2/Chapter2.htm ) that
indicates
that this occurs around a molar concentration of 3, but that seems
awfully high (pH of -.48?).


The website mentions 3M Cl(-) ion not the hydrogen ion concentration.
Did you mean pCl of -0.48? (pH is defined to be a positive number from
0 to 14; I don't think negative pH is of any use except as negative log
of a number greater than 1)
[/quote:af65976a3e]
I thought so too, but http://members.aol.com/profchm/pfactor.html
indicates:

For strong acid molar concentrations equal to or less than 1, the pH value
would have a value from 0-14.
One can have a pH that is a negative value in for example strong acid
solutions greater than 1 mole/liter.

So I am really confused. What I really want to know is if the Cl(-)
concentration of stomach acid (pH of about 1.5) is sufficient to allow any
significant solubility of AgCl.

Marshall
 
Farooq
Posted: Wed Dec 22, 2004 12:24 pm
 
Marshall Dudley wrote:
[quote:bafc3a8787]The website mentions 3M Cl(-) ion not the hydrogen ion
concentration.
Did you mean pCl of -0.48? (pH is defined to be a positive number
from
0 to 14; I don't think negative pH is of any use except as negative
log
of a number greater than 1)

I thought so too, but http://members.aol.com/profchm/pfactor.html
indicates:

For strong acid molar concentrations equal to or less than 1, the pH
value
would have a value from 0-14.
One can have a pH that is a negative value in for example strong acid
solutions greater than 1 mole/liter.
[/quote:bafc3a8787]
I wanted to say that we can have a negative pH mathematically; but note
that it was just a convineant scale of expressing hydrogen ion
concentration so if we have a concentration greater than 1 M [H(+)]; we
can not ignore acitivity coefficients and thus a 3 M HCl would not be
necessarily -log[3] but a number say 0.988 multpilied by 3. Also the pH
of 1 x 10^-7 M HCl would not be 7.

[quote:bafc3a8787]So I am really confused. What I really want to know is if the Cl(-)
concentration of stomach acid (pH of about 1.5) is sufficient to
allow any
significant solubility of AgCl.
[/quote:bafc3a8787]
Perhaps not significant but we can not ignore Cl(-) from our diet which
would be present in the stomach and the organic complexing agents in
our foods may increase the solubility silver.
This data might be helpful.
http://faculty.uccb.ns.ca/~dkeefe/chem200/math/1998/mathtutorial.htm:

AgCl(s) <--> Ag+(aq) + Cl-(aq) pKsp = 9.75
AgCl(s)<--> AgCl(aq) pK0 = 6.70
AgCl(s) + Cl-(aq) <--> AgCl2- (aq) pK1 = 4.70

Substitute the value of Cl(-) in stomach in K1 =
[AgCl2(-)]/[AgCl][Cl(-)]
and substitue AgCl by manipulating the first two equations. This might
give us a rough idea of solubility of silver chloride in stomach acid.
 
Wilco Oelen
Posted: Wed Dec 22, 2004 4:48 pm
 
farooq_w@hotmail.com wrote:
[quote:a9f2e41bf7]Marshall Dudley wrote:
The website mentions 3M Cl(-) ion not the hydrogen ion
concentration.
Did you mean pCl of -0.48? (pH is defined to be a positive number
from
0 to 14; I don't think negative pH is of any use except as
negative
log
of a number greater than 1)

I thought so too, but http://members.aol.com/profchm/pfactor.html
indicates:

For strong acid molar concentrations equal to or less than 1, the
pH
value
would have a value from 0-14.
One can have a pH that is a negative value in for example strong
acid
solutions greater than 1 mole/liter.

I wanted to say that we can have a negative pH mathematically; but
note
that it was just a convineant scale of expressing hydrogen ion
concentration so if we have a concentration greater than 1 M [H(+)];
we
can not ignore acitivity coefficients and thus a 3 M HCl would not be
necessarily -log[3] but a number say 0.988 multpilied by 3. Also the
pH
of 1 x 10^-7 M HCl would not be 7.

So I am really confused. What I really want to know is if the
Cl(-)
concentration of stomach acid (pH of about 1.5) is sufficient to
allow any
significant solubility of AgCl.

Perhaps not significant but we can not ignore Cl(-) from our diet
which
would be present in the stomach and the organic complexing agents in
our foods may increase the solubility silver.
This data might be helpful.
http://faculty.uccb.ns.ca/~dkeefe/chem200/math/1998/mathtutorial.htm:

AgCl(s) <--> Ag+(aq) + Cl-(aq) pKsp = 9.75
AgCl(s)<--> AgCl(aq) pK0 = 6.70
How should I interpret these two numbers? The first one, I assume is a[/quote:a9f2e41bf7]
measure, useful as solubility product, -log10([Ag(+)][Cl(-)])? Is the
other one a solubility "product" also (containing just one factor,
expressed as -log10([AgCl]))?

If I try to solve the equations for AgCl(s), added to pure water, then
I need a third equilibrium constant for
AgCl(aq) <---> Ag(+)(aq) + Cl(-)(aq),
otherwise I have too many unknowns. If I'm missing something, could you
please explain that to me?

My unknowns are:

[Ag(+)(aq)]
[Cl(-)(aq)]
[AgCl(aq)]

The species AgCl(s) is not part of the set of equations, see definition
of Ksp.


[quote:a9f2e41bf7]AgCl(s) + Cl-(aq) <--> AgCl2- (aq) pK1 = 4.70
Probably you also should have AgCl(aq) + Cl(-) <---> AgCl2(-)(aq). How[/quote:a9f2e41bf7]
is pK1 defined here? Is this -log10([AgCl2(-)(aq)]/[Cl(-)(aq)])?

[quote:a9f2e41bf7]
Substitute the value of Cl(-) in stomach in K1 =
[AgCl2(-)]/[AgCl][Cl(-)]
See above, is this the definition of K1? I think that you are 'mixing[/quote:a9f2e41bf7]
up' AgCl(s) and AgCl(aq).

[quote:a9f2e41bf7]and substitue AgCl by manipulating the first two equations. This
might
give us a rough idea of solubility of silver chloride in stomach
acid.[/quote:a9f2e41bf7]
Using this, I come up with four equations and four unknowns, not quite
easily solved by hand, but with some software it should not be that
difficult. My unknowns are:

[Ag(+)(aq)]
[Cl(-)(aq)]
[AgCl(aq)]
[AgCl2(-)(aq)]

Because of the fairly large concentration of Cl(-), the equations can
be simplified considerably safely, by assuming [Cl(-)] constant. Then
the system reduces to a set of three equations with the three aquated
Ag-species as unknowns.

Wilco
 
Borek
Posted: Thu Dec 23, 2004 4:35 pm
 
Wilco Oelen wrote:

[quote:96f3593008]AgCl(s) <--> Ag+(aq) + Cl-(aq) pKsp = 9.75
AgCl(s)<--> AgCl(aq) pK0 = 6.70
AgCl(s) + Cl-(aq) <--> AgCl2- (aq) pK1 = 4.70
(...)
If I try to solve the equations for AgCl(s), added to pure water, then
I need a third equilibrium constant for
AgCl(aq) <---> Ag(+)(aq) + Cl(-)(aq),
otherwise I have too many unknowns. If I'm missing something, could you
please explain that to me?
[/quote:96f3593008]
I would assume that for the reaction

AgCl(aq) <---> Ag(+)(aq) + Cl(-)(aq)

dissociation constant is

pK = pKsp - pK0

Best,
Borek
--
BPP Marcin Borkowski, ul. Architektów 14, 05-270 Marki
If you know someone with dyslexia take a look at http://www.bpp.com.pl
Remove your.pants to email me directly Smile
 
Wilco Oelen
Posted: Fri Dec 24, 2004 2:34 am
 
Borek wrote:
[quote:82d8eebb0e]Wilco Oelen wrote:

AgCl(s) <--> Ag+(aq) + Cl-(aq) pKsp = 9.75
AgCl(s)<--> AgCl(aq) pK0 = 6.70
AgCl(s) + Cl-(aq) <--> AgCl2- (aq) pK1 = 4.70
(...)
If I try to solve the equations for AgCl(s), added to pure water,
then
I need a third equilibrium constant for
AgCl(aq) <---> Ag(+)(aq) + Cl(-)(aq),
otherwise I have too many unknowns. If I'm missing something, could
you
please explain that to me?

I would assume that for the reaction

AgCl(aq) <---> Ag(+)(aq) + Cl(-)(aq)

dissociation constant is

pK = pKsp - pK0
Yes! Simple log-math! I have been thinking how to solve this problem[/quote:82d8eebb0e]
quite some time. Probably my brains already were in Xmas-mode!

PS: Farooq, this is the missing point. Using a relation, like the one
stated here makes solving the equations easier. In fact, the different
equilibria relations are not independent (mathematically speaking).
[quote:82d8eebb0e]
Best,
Borek
Thanks![/quote:82d8eebb0e]

Wilco
 
 
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