Potassium metabisulphite & Sodium hydroxide to form Potassium sulphite in solution?

[kozesluk]

From this fragment of text:

"L.P.Clerc and others indicate that Potassium Metabisulphite was the preferred source for the Sulphite in Rodinal, Potassium salts are used in preference to Sodium because of their greater solubility in water which becomes far more important in concentrated developer solutions. Metabisulphite and Hydroxide form Sulphite in solution."

I understand that the right amount of Potassium metabisulphite & Sodium hydroxide mixed in water should form a solution of Potassium sulphite.

something like: K2S2O5 + NaOH + H2O -> K2SO3 + something else?

The question is: does anyone know the right weights of both chemicals to form K2SO3? These chemical equations are hard for me since we don't have chemistry lessons (at least not of this kind) on electrical engineering university...

 

[Ian Grant]

add the detail

You need to add Potassium Hydroxide or you get a mixture of Sodium & Potassium Sulphite. It's simple to calculate by looking up the molecular weights.

I'll look at my notes:

K2S2O5 + 2 KOH ------> 2 K2S03 + H2O

As the Molecular weights are

KOH 56.11
Potassium Metabisulphite 222.32
Potassium Sulphite 158.26

222.32g Potassium Sulphite + 112.22g Potassium Hyroxide makes 316g Potassium Sulphite + 18.02g of water

So you just vary the quantities in proportion to make the desired amount

Ian

 

[kozesluk]

well, now it makes sense for me
thak you very much!