So I was doing electrolysis on two silver electrodes and sodium thiosulfate. Some observations

  • The voltage drops extremely fast from 2 V to less than 1 V in 15 minutes, possibly because of the thiosulfate reduction.

  • Gases are liberated out of solution.

  • The solution turns black quickly.

Alert: I am using a fume hood.

Since I'm afraid of this spoiled eggs smell I just want to know if I am in any way creating hydrogen sulfide? Just want to be sure that the gas is tetrathionate and not hydrogen sulfide.

My other concern is with the voltage. How can I keep it from dropping so fast?


Yup, you're forming sulfide.

Render the thiosulfate ion as $(\ce {S-}-\ce {SO3-})$. Then at the cathode:

$(\ce {S-}-\ce {SO3-})+2e^- \rightarrow \ce {S^{2-}}+\ce {SO3^{2-}}$

Both products are basic, with sulfide ion being strongly so, and they will react further with protons; so the sulfide ion gives some hydrogen sulfide. Sulfide ions can also combine with silver ions, from the anode, giving a black precipitate. The other product, sulfite ion, can be reduced further, possibly forming still more sulfide ion/hydrogen sulfide.

So the reaction is not safe. But kudos for using a fume hood.


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