Balancing Redox Reactions

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TeaK1C
Posts: 17
Joined: Fri Sep 25, 2015 3:00 am

Balancing Redox Reactions

Postby TeaK1C » Fri Feb 05, 2016 12:39 pm

When balancing redox reactions, when do you use H2O to balance it? How do you know to use H2O?

Angela Kim 2H
Posts: 13
Joined: Fri Sep 25, 2015 3:00 am

Re: Balancing Redox Reactions

Postby Angela Kim 2H » Fri Feb 05, 2016 2:20 pm

When balancing redox reactions, you always use H2O to balance out the Oxygens. In acidic conditions, you would then use H+ to balance the Hydrogens in the reaction.

Anthony Rosas 2K
Posts: 14
Joined: Fri Sep 25, 2015 3:00 am

Re: Balancing Redox Reactions

Postby Anthony Rosas 2K » Fri Feb 05, 2016 2:26 pm

When balancing a redox-reaction you use H2O to balance the oxygens. For example:
EQUATION: Br- + MnO4- ---> Br2 + Mn2+
STEP 1 (evaluate the charges):
Br-=(-1)|[Mn=(+7),O=(-2)]||Br2=(0)|Mn2+=(+2)
STEP 2 (separate the half reactions/balance electrons):
2Br- - 2e- ---> Br2
MnO4- + 5e- ---> Mn2+
STEP 3 (**add H2O to balance oxygen**):
2Br- - 2e- ---> Br2
MnO4- + 5e- ---> Mn2+ + 4H2O
STEP 4 (add H+ to balance hydrogen)
2Br- - 2e- ---> Br2
8H+ + MnO4- + 5e- ---> Mn2+ + 4H2O
STEP 5 (cancel the electrons and add the half reactions)
2Br- - 2e- ---> Br2 {2 mol e- so multiply by 5}
8H+ + MnO4- + 5e- ---> Mn2+ + 4H2O {5 mol e- so multiply by 2}

16H+ + 10Br- + 2MnO4- ---> 5Br2 + 2Mn2+ + 8H2O

Kayti Luu 2B
Posts: 19
Joined: Fri Sep 25, 2015 3:00 am

Re: Balancing Redox Reactions

Postby Kayti Luu 2B » Fri Feb 05, 2016 4:52 pm

When you write the half reactions to balance redox reactions, are we suppose to get rid of spectator ions. For example on the self test 14.1B question, it ask to write the balanced equation of acidified potassium permanganate solution reacting with sulfurous acid to form sulfuric acid and manganese (II) ions. In the solutions the potassium from the potassium permanganate is not present anywhere in the solution. Are we suppose to ignore it?


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