Redox question!

[NDPitch]

I'm having trouble with the below question. What are the half reactions here? My answer keeps coming out wrong. Any insight?



When the following reaction is balanced in acidic solution, what is the coefficient for NaBr?

H2SO4(aq) + NaBr(s) -------->>> Br2(l) + SO2(g) + Na2SO4(aq) + H2O(l)

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[NDPitch]

So this is what I have

2 (H2SO4 ) + 2NaBr------>Br2+ SO2+ Na2SO4+2H2O

That is correct. And I can get to that answer by just balancing the original reaction as you normally would. However, I'm confused because this is a redox reaction. Don't those have to be broken out into the half reactions, and then balance the electrons, hydrogens, oxygens, etc?

 

[NDPitch]

yeah so
reduction: 2e- + SO4 (2-) ---->SO2
Oxidation: 2Br- --> Br2 + 2e-

so there are only 2 e- that is being transfered. I don't think you need to solve the whole problem to find the answer to your question. So what I did is I broke down all the ionic parts into ions and crossed out the spectators like Na+ and then I saw that we need 2X SO4 (2-) because one of them was spectator and the other one got reduced. that was pretty much the key point to understand here I think. Besides you need to be able to discern that SO4 (2-) has S as 6+ and SO2 has S as 4+; so change of 2e-.

Hope that helps

Ahhh yes. I think I went wrong with SO4. I didn't factor in that it's -2. Those damn polyatomic ions!