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Homework Statement
Write the balanced chemical reactions in ionic and neutral forms for:
i) Enargite leaching by sodium bisulfide in basic solution to form chalcocite and thioarsenate.
ii) Oxygen pressure oxidation of As2S5 in acid solution to form scorodite. Assume all sulfide sulfur forms sulfate. (Assume that ferric ion is present in solution).
Homework Equations
N/A
The Attempt at a Solution
i) Cu3AsS4 + HS- = Cu2S + AsS43-
Balancing:
Cu3AsS4 + HS- = 3/2Cu2S + AsS43-
Cu3AsS4 + HS- = 3/2Cu2S + AsS43- +H+
Cu3AsS4 + HS- +e-= 3/2Cu2S + AsS43- +H+
? I cannot seem to balance the last equation properly. I do know that the e- present in the equation means that there should be 2 half reactions, not one as above, but cannot figure those out either.
ii) As2S5+O2 = AsO43-+SO42-
Left side:
As2S5 = AsO43-+SO42-
As2S5 = 2AsO43-+5SO42-
As2S5+28H2O= 2AsO43-+5SO42-
As2S5+28H2O= 2AsO43-+5SO42-+56H+
As2S5+28H2O= 2AsO43-+5SO42-+56H++40e-
Right side:
O2 = ?
O2 = 2H2O
O2 + 4H+= 2H2O
O2 + 4H++4e-= 2H2O
Add together (and cancel out e-):
As2S5+28H2O= 2AsO43-+5SO42-+56H++40e-
10*(O2 + 4H++4e-= 2H2O)
Ionic Form ===> As2S5+8H2O+10O2 = 2AsO43-+5SO42-+16H+
It is balanced (I checked).
But, I get into trouble when I try to get the neutral form. Nothing on the right requires ferric (the cation I use to put all aq terms into neutral form), thus there is an imbalance of iron. Also, how do I deal with the 2H2O that appears as part of scorodite? Do I just assume that it has become part of the solution?
EDIT: Figured out 1)ii) Use H+ (and NOT ferric, Fe3+) as the cation to turn products into neutral compounds (and thus the entire reaction into neutral form).
i.e. As2S5+8H2O+10O2 = 2H3AsO4+5H2SO4
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