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Difficult Half Equations

Hi, I'm really stuck on this question:
Give the half equations for the oxidation and reduction processes when manganese (VII) reacts with H2S, and use them to give the overall reaction equation.

So are these right?...
3e- + MnO4- + 8H+ --> Mn4+ +4H2O
8H2S ---> S8 + 16H+ + 16e-

If they are right, do I need to multiply the first equation by 16 and the bottom by 3, and put them together, (and then cancel out things on both sides) to get the full equation?

I'd really appreciate some help!! I think the reason I'm stuck is because the numbers get quite big and it just looks wrong.

Reply 1

Borek

Your half reactions are correctly balanced, but it doesn't make them OK. I am not convinced it is possible to answer the question without additional information about pH.

First equation depends on pH - in low pH permanganate gets reduced to Mn²⁺, in neutral to MnO₂, in high just to manganate.

No idea about the second. Mild oxidizers will get you to sulfur, but I think strong ones can oxidize sulfide to sulfate.