Na2S2O5 is smb. Hydrosulfite, Na2S2O4 if formed, reduces gold in alkaline environment if at all formed. (To produce it zinc is needed)
You didn't understand my topic correctly
Na2S2O4 is sodium hypodisulfite. It cannot be formed here.
Hydrosulfite has this formula: NaHSO3. In English, it is also called: Sodium bisulfite.
Slightly different meaning, mea culpa
Three ways of reactions :
(a)SO2-inducted Au reduction, (b)forming hydrosulfite (bisulfite), and (c) direct SMB (Na2S2O5 + HCl) reaction, NOT with hydrosulfite. I didn't call SMB as "hydrosulfite". I thought that Na2S2O5 is obviously SMB for readers.
All these reactions go at different speeds that's why can shift acidity unpredictably fast.
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