Obtaining a concentrated aqueous solution of potassium sulfite

bnxvs · Sep 15, 2020

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Obtaining a concentrated aqueous solution of potassium sulfite - sulfite, concentrate, solubility, developer, rodinal, potassium

To obtain a concentrated aqueous solution of potassium sulfite, you will need:
- potassium metabisulfite (it is best to buy it in wine shops)
- potassium hydroxide (caustic potassium)
K2S2O5 + 2KOH → 2K2SO3 + H2O

In water, metabisulfite is converted to an acidic salt of potassium hydrosulfite and reacts with potassium hydroxide to form 2 sulfite molecules.
Molar mass of potassium metabisulfite: 222.3236 g / M
Molar mass of potassium hydroxide: 56.10564 g / M
Molar mass of potassium sulfite:...

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Alan Johnson · Sep 15, 2020

http://www.jihaichem.com/template/cpa03-en.htm
The commercial product appears to have a pH of 9 - 9.5 so is that what should be aimed for in view of possible minor impurities in the starting materials hydroxide and metabisulfite?

bnxvs · Sep 15, 2020

In fact, I would rather rely not on pH, but on the results of titration of starch solution with iodine. But for the purposes of photochemistry, fortunately, such accuracy is not always necessary. Roughly you can focus on pH 8.9-9.2.

bnxvs · Sep 15, 2020

Finding quality metabisulfite is a much bigger problem. Unfortunately, many vendors sell an old, highly oxidized product. I got the best results with food metabisulphite, which is sold to winemakers. It is most often fresher and cleaner, as food products are controlled more thoroughly.

Alan Johnson · Sep 15, 2020

Some liquid concentrates like HC 110 (new) and DD -X contain Potassium Sulfite.

Obtaining a concentrated aqueous solution of potassium sulfite

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