Redox reaction

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AlyssaYeh_1B
Posts: 100
Joined: Sat Aug 17, 2019 12:16 am

Redox reaction

Postby AlyssaYeh_1B » Fri Feb 14, 2020 4:33 pm

For the example we looked at in class today (permanganate and iron), how come the oxidation numbers of hydrogen and oxygen don't change? How do we tell which ones were oxidized/reduced?

Annie Chantasirivisal_4G
Posts: 114
Joined: Wed Sep 18, 2019 12:21 am

Re: Redox reaction

Postby Annie Chantasirivisal_4G » Fri Feb 14, 2020 5:55 pm

The way I like to visualize it is by separating the molecules by element in order to determine their oxidation numbers.

For reference: 8H+ + MnO4- + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O

Oxygen and Hydrogen remained the same because when you separate them in H2O on the right, you can see that there are two H for every one O, which boils down to H having a +1 charge and O having a 2- charge, which is the same as the left with the H in 8H+ each having a +1 charge as well. O is a little harder to tell but if you recall from class Dr. Lavelle mentioned Mn on the left having a +7 charge, which would mean that each O must have a 2- charge in order to cancel out with Mn and result in the overall -1 charge of the molecule MnO4- (7+(4 x -2)=-1).

Mn and Fe, however, did change because Mn went from +7 on the left to +2 on the right, while Fe went from +2 on the left to +3 on the right.

In general, on the periodic table groups 1 and 2 will have charges +1 and +2, respectively, while groups 16 and 17 will have charges -2 and -1, respectively. The transition metals such as Mn and Fe vary with charge.

Thus, when you apply definitions of oxidation and reduction, MnO4- was reduced because going from +7 on the left to +2 on the right means that it has gained 5 electrons and caused its oxidation number to go down/become less positive, while 5Fe2+ was oxidized because going from +2 on the left to +3 on the right means that it lost an electron and caused its oxidation number to go up/be more positive.

I hope this helps!

chari_maya 3B
Posts: 108
Joined: Sat Sep 07, 2019 12:18 am

Re: Redox reaction

Postby chari_maya 3B » Fri Feb 14, 2020 6:16 pm

This was very helpful! I had the same question.

005324438
Posts: 51
Joined: Sat Aug 24, 2019 12:16 am

Re: Redox reaction

Postby 005324438 » Fri Feb 14, 2020 6:17 pm

For the most part, O will always be -1, halogens will always be -1, and H will always be +1. Once we assign values to these elements, then the rest we just add up the rest of the molecule to equal the total charge.

Lauren Tanaka 1A
Posts: 109
Joined: Sat Aug 17, 2019 12:18 am

Re: Redox reaction

Postby Lauren Tanaka 1A » Sat Feb 15, 2020 10:20 am

I think you can look at the elements within a compound where you know the oxidation numbers and based on the total net charge of the molecule you can figure out the number for those elements you don't know.

Sydney Myers 4I
Posts: 100
Joined: Fri Aug 09, 2019 12:17 am

Re: Redox reaction

Postby Sydney Myers 4I » Sat Feb 15, 2020 12:11 pm

005324438 wrote:For the most part, O will always be -1, halogens will always be -1, and H will always be +1. Once we assign values to these elements, then the rest we just add up the rest of the molecule to equal the total charge.


I think Oxygen's oxidation states is usually -2, not -1.


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