13.3 b Reducing/Oxidizing Agent

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Madison Davis 3F
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Joined: Fri Sep 26, 2014 2:02 pm

13.3 b Reducing/Oxidizing Agent

Postby Madison Davis 3F » Fri Feb 06, 2015 2:00 pm

For the reaction MnO4- +H2SO3 --> Mn2+ +HSO4-

the solutions manual says that MnO4- is the oxidizing agent and H2SO3 is the reducing agent.

Why is this? I realize that the oxidizing agent is the one being reduced, and the reducing agent is the one being oxidized, and that oxidation is the loss of electrons, and reduction is the gaining of electrons...I'm just bad at telling which is which sometimes...Some explanation would be very helpful!

Thank you!

Niharika Reddy 1D
Posts: 127
Joined: Fri Sep 26, 2014 2:02 pm

Re: 13.3 b Reducing/Oxidizing Agent

Postby Niharika Reddy 1D » Fri Feb 06, 2015 3:25 pm

As you said, the oxidizing agent (OA) is itself reduced, and the reducing agent (RA) is itself oxidized. The OA causes the oxidation of the other species since it wants the electrons the species it oxidizes will give off, which it will then gain, causing the OA itself to be reduced.

After you determine which half reaction is the oxidation half reaction, the reactant losing electrons in the oxidation half reaction written the correct way (the opposite of the reduction half reaction; with the electrons being lost, so electrons present as products) will be the RA.

Looking at it in terms of oxidation numbers, the species that has an atom that increases in oxidation number is the RA and that which has an atom that decreases in oxidation number is the OA.

Satvir Saggi 1I
Posts: 22
Joined: Fri Sep 26, 2014 2:02 pm

Re: 13.3 b Reducing/Oxidizing Agent

Postby Satvir Saggi 1I » Fri Feb 06, 2015 3:38 pm

I recommend looking at the individual oxidation numbers for the element. (Attached is a list of common oxidation numbers):

For MnO4-, we know that the oxidation number of O is -2 and the total sum of the oxidation numbers of each element has to equal the charge of polyatomic ion (-1). Therfore, x+4(-2)=-1 and x=7. The oxidation number of Mn in MnO4- is 7. Finally, compare the oxidation number of Mn in the reactants side to the oxidation number of Mn to the products side. As you can see, the oxidation number decreases from 7 to 2. Therefore, Mn is being reduced since a decrease in the oxidation number of a species signifies that it is being reduced. Since MnO4- is the overall species being reduced, it is consequently the oxidizing agent.
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