Sulfuric Acid & Gold: Does it React?

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Discussion Overview

The discussion centers around the interaction between concentrated sulfuric acid and gold, specifically whether sulfuric acid can react with gold despite the oxidation potential of sulfur being higher than that of gold. Participants explore the electrochemical properties and reduction potentials involved in this scenario.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that concentrated sulfuric acid does not react with gold, despite the higher oxidation potential of sulfur in concentrated H2SO4.
  • Another participant suggests rechecking the standard reduction potentials for sulfuric acid and metallic gold to determine which species is more likely to be reduced.
  • A participant provides specific half-reactions and their corresponding standard reduction potentials, indicating that the overall reaction would be non-spontaneous due to a negative resulting E value.
  • One participant questions the clarity of the previous comments regarding the potential of S2O7 in oleum, asking for clarification on whether the potential is presented as an oxidation or reduction potential and requesting the exact electrochemical potential involving oleum.

Areas of Agreement / Disagreement

Participants express differing views on the reactivity of sulfuric acid with gold, with some supporting the idea that gold does not react while others raise questions about the implications of oxidation potentials. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the electrochemical potentials and the specific conditions under which these reactions are considered, particularly concerning the nature of oleum and its role in the reactions discussed.

haiha
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Hi everybody
I know that concentrated sulfuric acid doesn't react gold. But I am puzzled because the oxidation potential of sulfure in concentrated H2SO4 is even higher than that of gold. Could anyone help me please.
Thanks
 
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haiha,
Recheck the standard reduction potentials for acidic sulfuric acid and of metallic gold. Which one would more tend to want to be in reduced form?

1 sulfate + 4 H+ + 2e -----> sulfurous acid + 1 water, E = +1.5 v

1 auric(+3) + 3e -----> 1 gold in reduced metal form, E = +.17 v

Now, I forgot how the rest of this works, but you probably want to balance the two half reactions and find the resulting new "E" value; and you will find that it is negative, meaning the reaction is not spontaneous. You must use more energy in order to dissolve the gold than would be provided just from sulfuric acid.
 
Thanks symbolipoint for answering me. But when i check in the manual, the potential of S2O7 (which is in oleum) is about 1.9-2.0 v (i don't remember exactly), and that is higher than that of metalic gold.
 
haiha said:
Thanks symbolipoint for answering me. But when i check in the manual, the potential of S2O7 (which is in oleum) is about 1.9-2.0 v (i don't remember exactly), and that is higher than that of metalic gold.

Your comments there aren't exactly so clear. Are you giving the "oleum" reduction potential or are you giving it as an oxidation potential? What is the expected other form starting from "oleum"? Be aware, oleum is a solution of sulfur trioxide in sulfuric acid; no water is present. Would you give the exact electrochemical potential involving oleum? That might help see the situation more clearly. (I could not find that in an online search and it's not in my old textbook).
 

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