Chemical Forums

Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Pipo87 on January 12, 2015, 01:39:58 PM

Title: Redox reaction, can't seem to balance ethanol + manganate
Post by: Pipo87 on January 12, 2015, 01:39:58 PM
Hello

I'm trying to balance the following reaction (in acid):

CH3CH2OH + MnO42-  --> CO2 + Mn2+

I can balance the half reaction for manganate (oxidant), that one is easy:

8H+ + MnO42- + 4e- <> Mn2+ + 4H2O

But the halfreaction for ethanol (reductant) just doesn't seem right, I can't balance it:

H2O + CH3CH2OH <> 2CO2 + 8H+ + 7e- + 5e-

The mass is balanced this way, but the electric charges aren't, I can't figure out how :(

Probably should note that I'm a first grade chemistry student, the reaction I'm trying to balance is for school work

Thanks for any help at all!
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: Pipo87 on January 12, 2015, 01:53:49 PM
Never mind I missed something completely, and that is that the O's weren't balanced yet
so it's like this:

3H2O + CH3CH2OH <> 2CO2 + 12H+ + 7e- + 5e-
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: unsu on January 13, 2015, 02:46:31 PM
The half-reaction for the permanganate that you wrote is not correct.
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: mjc123 on January 13, 2015, 05:13:02 PM
It was manganate, not permanganate. Though the oxidation state diagram that I posted here http://www.chemicalforums.com/index.php?topic=78280.0
would suggest that in acid it is unstable to disproportionation to MnO4- and MnO2.
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: Babcock_Hall on January 13, 2015, 07:32:41 PM
One thing you need to correct is the charge on the permanganate ion.
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: Borek on January 14, 2015, 02:40:07 AM
Quote from: Babcock_Hall on January 13, 2015, 07:32:41 PM
One thing you need to correct is the charge on the permanganate ion.

As mjc already wrote - question asks for manganate, not permanganate, and the formula of magnanate is OK.

Quote from: mjc123 on January 13, 2015, 05:13:02 PM
in acid it is unstable to disproportionation to MnO4- and MnO2.

I don't think it matters much for the final answer. While it would mean there are two possible paths for the oxidation, final (overall) reaction equation would be the same.
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: unsu on January 14, 2015, 09:05:18 AM
Quote
It was manganate, not permanganate.

Sorry, it did not notice that. Normally people use permanganate to oxidize organic substrates, I never saw anyone using manganate to oxidize the substrates. But anyway, I would like Pipo87 to comment on this to make sure this wasn't a mistake :)
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: Pipo87 on January 14, 2015, 05:18:49 PM
It wasn't a mistake, it really is manganate :p
I also noticed permanganate it much more common, when I tried googling for this reaction before. Actually I did not find any results at all for this reaction with manganate

Though it's not a reaction we used in practice, just a theoretical exercise i had to complete.

Thanks for the feedback anyways, but as I posted before, I managed to find my own silly mistake already
Title: Re: Redox reaction, can't seem to balance ethanol + manganate
Post by: Babcock_Hall on January 14, 2015, 06:20:11 PM
Quote from: mjc123 on January 13, 2015, 05:13:02 PM
It was manganate, not permanganate. Though the oxidation state diagram that I posted here http://www.chemicalforums.com/index.php?topic=78280.0
would suggest that in acid it is unstable to disproportionation to MnO4- and MnO2.
mjc,

How realistic is the question as written?