Sodium carbonate solvent properties

[lensmagic]

Does sodium carbonate have solvent properties (a la sodium sulfite and sodium chloride) in a film developer?

 

[rwboyer]

Not really from anything I have ever seen it is an alkali (manly used as an accelerator)

Why?

RB

 

[lensmagic]

I am aiming toward an "acutance" film developer, and want to use an alkali (accelerator) that doesn't possess solvent properties.

 

[rwboyer]

I am aiming toward an "acutance" film developer, and want to use an alkali (accelerator) that doesn't possess solvent properties.

Well most common alkalis, if they are "solvent", do not appear to have any effect at useful concentrations in developer that I know of. Sodium carbonate is a common alkali in some developers that are very high acutance - like Kodak D-1/ABC pyro.

RB

 

[Alan Johnson]

The molar concentrations of dissolved ions are multiplied together to give the solubility product.The solubility product of silver carbonate is less than that of silver chloride by a factor of about 23:
www.csudh.edu/oliver/chemdata/data-ksp.htm

 

[Kirk Keyes]

Alan - how does your post answer the original question about silver solvents? You show that silver carbonate is less soluble in water than silver chloride, but not if it is a silver solvent or not.

Look at silver sulfite - it has a solubility product of 1.5 x 10-14, that makes silver sulfite less soluble than either silver chloride, silver carbonate, and even silver bromide - yet sulfite ion is a silver solvent. Silver cyanide is even less soluble, Ksp = 1.2 x 10-16, yet cyanide ion is a silver solvent.

Formation of a complex is the key to the action of chloride and cyanide as silver solvents.

 

[Alan Johnson]

Kirk, I believe you are right.
From Photographic Processing Chemistry by LFA Mason p113:"A high rate of solution of the silver halide is necessary if a high proportion of of physical development is required.One must therefore select a complexing agent whose silver complex has a high stability constant,and it must be present in sufficient concentration to complex the silver halide as rapidly as the complex is catalytically reduced."
Since this is the opposite of what is required in an acutance developer,where chemical rather than physical development is wanted,for an acutance developer perhaps carbonate does not significantly complex in this way and is not solvent.

 

[Kirk Keyes]

I don't have a copy available right now, but I think James and Mees has a table of silver complexes and their stability listed in it. It should give a more definitive answer.

 

[Photo Engineer]

Sodium Carbonate has no Silver complexing ability whatsoever!

PE

 

[Kirk Keyes]

It should give a more definitive answer.

I should have said it should give a more definitive answer to other complexing agents. (And certainly carbonate is not one of them.)