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Author Topic:   Help on redox reactions
NoNukes
Inactive Member


Message 2 of 8 (707602)
09-29-2013 12:12 AM
Reply to: Message 1 by yenmor
09-28-2013 11:09 PM


Write half reactions.
Balance elements in each half reactions except H and O's last
.you add h20 when you need to balance oxygen on the other side.
you add h+ when you need to balance H's on the other side. This can happen because of adding those h2Os.
Then balance charges by adding electrons to each half reaction.
etc...
In basic soln' once finished add OH to each side to form water with each H+.
Edited by NoNukes, : No reason given.

Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.
Richard P. Feynman
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass

This message is a reply to:
 Message 1 by yenmor, posted 09-28-2013 11:09 PM yenmor has replied

Replies to this message:
 Message 3 by yenmor, posted 10-02-2013 12:12 AM NoNukes has replied

  
NoNukes
Inactive Member


Message 4 of 8 (707908)
10-02-2013 1:13 AM
Reply to: Message 3 by yenmor
10-02-2013 12:12 AM


Ok, please demonstrate for us how you would go about balancing the following with half reactions like you said.
Who is us?
What is giving you trouble? Can you not identify the two half reactions? You ignore the h+ and the water and then write down the two half reactions using what is left. one half reaction involves Mn, the other has Cr, C, and N.
Sure the problem tedious, but aren't you using a computer?
Balance every element except H,O
2Cr7N66H96C42O24 = 7Cr2O7-2 + 84CO2 + 132NO3-
MnO4 = Mn+2
Now balance the O using H20.
Then balance the H using H+
2Cr7N66H96C42O24 + 565 H2O = 7Cr2O7-2 + 84CO2 + 132NO3- + 1322 H+
MnO4- + 8H+ = Mn+2 + 4H2O
The rest requires a bunch of tedious arithmetic and nothing more. Do you really need me to do that stuff?
Then add e- as needed to each half reaction so each half reaction has balanced charges. If electrons are on the same side in the two half reactions, then it wasn't an ox-redox. Quit.
2Cr7N66H96C42O24 + 565 H2O = 7Cr2O7-2 + 84CO2 + 132NO3- + 1322 H+ + 1176e-
MnO4- + 8H+ +5e- = Mn+2 + 4H2O
Multiplty each equation by whatever required so that each half reaction involves the same number of electrons. (5 and 1176 respectively) then add two half reactions, remove species that are on two sides of equation. This should clear out all electrons. Clear fractions as needed. Reduce if possible. Done
I believe the answer in your display is correct, but I did not do a complete check.
Edited by NoNukes, : No reason given.
Edited by NoNukes, : No reason given.

Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.
Richard P. Feynman
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass

This message is a reply to:
 Message 3 by yenmor, posted 10-02-2013 12:12 AM yenmor has replied

Replies to this message:
 Message 5 by yenmor, posted 10-02-2013 5:34 AM NoNukes has replied

  
NoNukes
Inactive Member


Message 6 of 8 (707917)
10-02-2013 8:22 AM
Reply to: Message 5 by yenmor
10-02-2013 5:34 AM


One question. Do you always add the H+ on the left side and the H2O on the right side?
No. That is not even true for the example I worked. You add the H2O on the side opposite from the excess oxygen. Then you add H+ to balance the excess Hs.
And don't forget the extra rule at the end for basic solutions. The steps I used above assumed an acidic solution.
Good luck with your presentation.

Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.
Richard P. Feynman
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass

This message is a reply to:
 Message 5 by yenmor, posted 10-02-2013 5:34 AM yenmor has not replied

Replies to this message:
 Message 7 by NoNukes, posted 10-02-2013 1:58 PM NoNukes has not replied

  
NoNukes
Inactive Member


Message 7 of 8 (707945)
10-02-2013 1:58 PM
Reply to: Message 6 by NoNukes
10-02-2013 8:22 AM


Rule exceptions...
I thought I would mention at least one rule exception.
When you have something like this
O- ==> O2
You don't balance it by adding H2O. You just adjust the coefficients.

Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I believe that a scientist looking at nonscientific problems is just as dumb as the next guy.
Richard P. Feynman
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass

This message is a reply to:
 Message 6 by NoNukes, posted 10-02-2013 8:22 AM NoNukes has not replied

Replies to this message:
 Message 8 by onifre, posted 10-02-2013 11:59 PM NoNukes has not replied

  
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