Reducing and Oxidizing agents

[metukah]

What is the fastest way of determining what is the reducing agent and oxidizing agent in this equation:

2HCl + H2O2 + MnO2 ---> O2 + MnCl2 + 2H2O

Do you have to figure out the oxidation number for each reactant and then see how this changed in the products? This seems too time consuming. Is there a trick?

Thanks!

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[AlexB]

What is the fastest way of determining what is the reducing agent and oxidizing agent in this equation:

2HCl + H2O2 + MnO2 ---> O2 + MnCl2 + 2H2O

Do you have to figure out the oxidation number for each reactant and then see how this changed in the products? This seems too time consuming. Is there a trick?

Thanks!

Ah that makes two of us confused dods. I'm curious to hear a faster solution as well.

 

[MCAT4life]

I was wrong!! but at least i tried lol..

 

[loveoforganic]

Sorry, but that's not right.

The autodecomposition of hydrogen peroxide to water and oxygen is a redox reaction - oxygen goes from -1 in H2O2 to -2 in H2O and 0 in O2. This is a disproportionation reaction.

HCl is not an oxidizing or reducing species here.

H2O2 acts as a reducing agent here, and MnO2 acts as the oxidizing agent.

In each species, oxygen is being oxidized (-1 -> 0) and manganese is being reduced (+4 -> +2).

 

[MCAT4life]

I'm just wondering, why would I look at the oxidation state of the Oxygen rather than the Hydrogen to determine the change in oxidation state in this case?

 

[loveoforganic]

Hydrogen doesn't change oxidation state here.

 

[luctoretemergo]

Hydrogen doesn't change oxidation state here.

Isn't H +2 when with peroxides?

 

[Silverfalcon]

Isn't H +2 when with peroxides?

No.

There is actually no such case - that I know of - in which hydrogen has +2 oxidation state. It is almost always +1 unless it is a part of metal hydride (LiH or NaH for example) that it becomes -1.

The change in oxidation states here is with oxygen, which becomes -1 instead of -2. This is one of the few exceptions that you may have learned in your laboratory courses (hydrogen peroxide is a commonly discussed compound).

Reference source (if interested):

http://www.science.uwaterloo.ca/~cchieh/cact/c123/oxidstat.html

 

[loveoforganic]

Hydrogens only have a single proton. It's impossible for them to be +2.

 

[luctoretemergo]

Hydrogens only have a single proton. It's impossible for them to be +2.

Yea I was mistaking it for oxygen in peroxides, which are -1, my bad.