[alt-photo] Re: Stoichiometry for the nonscientist

[EJ Photo]

Loris, My measurements of store bought potassium oxalate is much closer to 5
if I recall, but that was many years back. Are you mixing that with
distilled water? Different makers may give you different pH ranges. The Alfa
Aesar book at my fingers does not give me a pH of a solution. 


Eric Neilsen
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-----Original Message-----
From: alt-photo-process-list-bounces at lists.altphotolist.org
[mailto:alt-photo-process-list-bounces at lists.altphotolist.org] On Behalf Of
Loris Medici
Sent: Wednesday, August 04, 2010 12:05 PM
To: The alternative photographic processes mailing list
Subject: [alt-photo] Re: Stoichiometry for the nonscientist

18% Potassium Oxalate: K2C2O4, 166.216g/mol, 180g (in final volume of
1000ml) / 166.216  = 1.083M solution.

1. 1.083 mol K2CO3 (mol. mass = 138.206g) = 1.083M x 138.206g/mol ~= 150g

2.a. 1.083 mol "anhydrous" C2O4H2 (mol. mass = 90.035g) = 1.083M x
90.035g/mol = 97.5g
    OR
2.b. 1.083 mol C2O4H2.2H2O  (that's "dihydrate" - mol. mass = 126.066g) =
1.083M x 126.066g/mol ~= 136.5g

for a total / final solution volume of 1000ml.

Yes, your figures are right.

BTW, you'll have to add some more oxalic acid to set the pH to something
around 5... (You add in small amnts, test with a strip of pH test paper.)
Potassium oxalate alone will give a pH around 8 (if I'm not mistaking), and
you don't want that!

Regards,
Loris.


On 04.Ağu.2010, at 18:50, David Ashcraft wrote:

> My past post:
>> OK - What if I needed to mix a formula like: 180 gms potassium oxalate
K2C204.H2O mixed with water to make 1 liter.  I only have potassium
carbonate and oxalic acid on hand.
>> 
>> I know that I can make this formula of potassium oxalate by mixing
potassium carbonate and oxalic acid; PC is K2CO3 and OC is C2H204.  Now how
would I know how much of each of these to make up my original formula?
> 
> 
> And now after some tricky shenanigans I arrive at: 149.64 g of K2CO3 and
97.59 g of C2H2O4
> Would anybody agree?
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