How do I balance long redox equations?

Question

I can balance half and full redox equations but I struggle to balance an equation once other elements are thrown in between like I can balance the reduction and oxidation sides fine but what do I do with the original other elements which did not play a part in the two half equations but were there right at the start?

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Answer 1 · 2018-03-21T10:25:48

You assign oxidation states or average oxidation states to the original carbons...

You got #C_6H_8O_6#...the average oxidation state of carbon is here #+2/3#...agreed?

You finish with #C_6H_6O_6#...the average oxidation state of carbon is #+I#...and so clearly the carbon has been oxidized...

Are you clear on how I assigned those numbers?

And so....

#C_6H_8O_6rarrC_6H_6O_6+2H^+ +2e^(-)# #(i)#

And meanwhile #"nitrite anion"#, #NO_2^(-)#, i.e. #N(+III)# is REDUCED to #NO#, #N(+II)#...

#NO_2^(-) +2H^+ + e^(-) rarr NO(g)+H_2O# #(ii)#

And so we add #(i)+2xx(ii)#

#C_6H_8O_6+2NO_2^(-) +4H^+ + 2e^(-)rarrC_6H_6O_6+2NO(g)+2H_2O+2H^+ +2e^(-)#

...and cancel away...

#C_6H_8O_6+2NO_2^(-) +2H^+ rarrC_6H_6O_6+2NO(g)+2H_2O#

Does this address what you want? I am not entirely clear...