Could someone explain this redox problem?

Since manganese goes from a +4 to +2 oxidation state, it does that mean MnO2, as a whole is being reduced making it an OXIDIZING reagent. Why? Because MnO2's gaining of electrons CAUSES the oxidation of a different compound.

So we need to find this other compound that balances out this oxidizing agent- the reducing agent. Using the same idea as above, reducing agent is the compound that goes through oxidation. In this case, that would be H2O2, where H has an oxidation state of +1 and Oxygen has an oxidation state of -1 (to make the total oxidation state 0). If you look on the right side, O2 allows the Oxygen to have an oxidation state of 0. So, Oxygen is actually being oxidized in the process by the following (simplified):

Oxidation:
O(with -1e) --> O (with neutral charge) + e- (electron that is lost)

Which makes H2O2 the reducing agent. You can also use process of elimination to get to choice D. A and B don't work because we know that MnO2 is the oxidizing agent, which leaves us with choice C and D. We can take a look at choice C, and realize that H or Cl don't change oxidation states in the process (they always stay +1 and -1 respectively), which leaves us with choice D.

Hope that helped.

how do you know that the peroxide isn't actually being reduced to water, instead of being oxidized to O2?

I thought given that you know manganese's change in oxidation state, it is technically only the manganese that is getting reduced and is the oxidizing agent.

HCl can be ignored since neither H or Cl changes oxidization states

peroxide's O has to be oxidized to 02/be the reducing agent because that's what redox is. there needs to be reduction and oxidization.

Hahah i missed that one too, I was kind of ticked because it knocked me from a 14 to a 13

cheezer said:

I thought given that you know manganese's change in oxidation state, it is technically only the manganese that is getting reduced and is the oxidizing agent.

HCl can be ignored since neither H or Cl changes oxidization states

peroxide's O has to be oxidized to 02/be the reducing agent because that's what redox is. there needs to be reduction and oxidization.

Click to expand...

Agreed.