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Topic: Method for balancing this equation  (Read 3511 times)

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Offline mous

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Method for balancing this equation
« on: January 21, 2012, 09:04:45 PM »
C3H8O + CrO3 + H2SO4 = Cr2(SO4)3 + C3H6O + H2O

I've balanced this equation for mass and this was the result:

3C3H8O + 2CrO3 + 3H2SO4 = Cr2(SO4)3 + 3C3H6O + 6H2O

I was wondering how this would be done using the redox method.
These are the oxidation numbers I found (for the respective elements above):
(+2, +1, -2) + (+6,-2)+ (+1, +6, -2) = (+3, +6, -2) + (-4/3, + 1, -2) + (+1, -2)

Carbon and Chromium are the elements undergoing redox. However, both are gaining electrons, and that does not make sense to me. (Chromium gains 3 from +6 to +3; Carbon gains 3 1/3 from +2 to -4/3) And there is no way to balance the electron transfer since 3 and 3 1/3 have no common multiple.

Is it possible to balance this equation using the redox method?
I was also thinking about the ion electrode method, but as far as I know, that is mostly used if charges are in the equation, and there are none in this equation. Is it valid to balance this equation using the ion electrode method?

Offline Hunter2

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Re: Method for balancing this equation
« Reply #1 on: January 22, 2012, 09:38:52 AM »
You have to develop the single Oxidation and Reduction reaction.
Rule: Reduction add H+ on Educt side, get water on product side
Oxidation vise versa.

Example MnO4- + 8 H+ + 5 e- => Mn2+ + 4 H2O

Try yourself with your given example.

Offline mous

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Re: Method for balancing this equation
« Reply #2 on: January 22, 2012, 09:28:55 PM »
You have to develop the single Oxidation and Reduction reaction.
Rule: Reduction add H+ on Educt side, get water on product side
Oxidation vise versa.

Example MnO4- + 8 H+ + 5 e- => Mn2+ + 4 H2O

Try yourself with your given example.

My result:
C3H8O = C3H6O + 2H+ + 2e- (x3)

6H+ + 6e- + 3H2SO4 + 2CrO3 = Cr2(SO4)3 + 6H2O

6H+ +6e- + 3H2SO4 + 2CrO3 + 3C3H8O = Cr2(SO4)3 + 6H+ + 6H2O + 3C3H6O + 6H+ + 6e-

3H2SO4 + 2CrO3 + 3C3H8O = Cr2(SO4)3 + 6H2O + 3C3H6O


Offline Hunter2

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Re: Method for balancing this equation
« Reply #3 on: January 23, 2012, 03:13:30 AM »
You had on 6 H+ to much.

But the result is correct. Normally the SO42- will not used in the equation, because in sulfuric as well in the chromiumsulfate they are the same.

Offline mous

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Re: Method for balancing this equation
« Reply #4 on: January 23, 2012, 04:10:54 PM »
Thanks for catching the typo, and thanks for your help. :)

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