In photography, unexposed silver bromide is removed from film by soaking the film in a solution of sodium thio?

I would suggest referring back to your notes (and/or text books) covering that subject. Maybe contact the manufacturer of the chemicals.

This question would be better placed in the Chemistry/Science or Math section. Photographers don't worry about things like this as a rule, they take it on faith that the whole thing is gonna work. Maybe RIT and Brooks (in the old days) taught the chemistry aspect to this level in the US. In Germany, one has to know this to even call oneself a photographer - there are strict laws - most photogs in the US would not qualify to call themselves photographers as a business classification under German standards.