Thiosulphate + sulphuric acid

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Offline lightarrow

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Thiosulphate + sulphuric acid
« on: 23/09/2007 10:24:06 »
What happens mixing diluted H2SO4 to a water solution of Na2S2O3?

Edit: Sorry, I wrote Na2S2O4 as a mistake. It's corrected now.
« Last Edit: 24/09/2007 15:17:32 by lightarrow »

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Offline DrDick

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Thiosulphate + sulphuric acid
« Reply #1 on: 25/09/2007 17:14:43 »
from the Wikipedia article on sodium thiosulfate:

Quote
Thiosulfate anion characteristically reacts with dilute acids to produce sulfur, sulfur dioxide and water:[1]

    S2O32−(aq) + 2H+ (aq) → S(s) + SO2(g) + H2O(l)


So it's not that it needs sulfuric acid - any acid will do.  Sulfuric acid can act as a weak oxidizing agent in the right circumstances, but this isn't it.  In fact, the thiosulfate ion is actually its own oxidizing and reducing agent in acid.  The two sulfur atoms exist in different oxidation states, with an average of +2.  One sulfur atom then goes to +4 while the other goes to zero.

Dick

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Thiosulphate + sulphuric acid
« Reply #2 on: 25/09/2007 19:24:02 »
from the Wikipedia article on sodium thiosulfate:

Quote
Thiosulfate anion characteristically reacts with dilute acids to produce sulfur, sulfur dioxide and water:[1]

    S2O32−(aq) + 2H+ (aq) → S(s) + SO2(g) + H2O(l)


So it's not that it needs sulfuric acid - any acid will do.  Sulfuric acid can act as a weak oxidizing agent in the right circumstances, but this isn't it.  In fact, the thiosulfate ion is actually its own oxidizing and reducing agent in acid.  The two sulfur atoms exist in different oxidation states, with an average of +2.  One sulfur atom then goes to +4 while the other goes to zero.

Dick
Thank you. I indeed imagined a dismutation could happen; you have confirmed it. That is a way to produce colloidal sulfur particles in water for experiments in optics.

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Offline DrDick

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Thiosulphate + sulphuric acid
« Reply #3 on: 25/09/2007 20:22:49 »
Actually, I believe that was the next line in the Wikipedia article.   [:)]

Dick

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Offline lightarrow

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Thiosulphate + sulphuric acid
« Reply #4 on: 26/09/2007 15:06:45 »
Actually, I believe that was the next line in the Wikipedia article.   [:)]

Dick
That's true. I had only read the italian version. Thank you.