Balancing Redox Reactions in Acid and Basic Solutions

[sbhit2001]

I understand the concept of balancing chemical equations but in the case of redox reactions I don't understand the physical meaning of balancing in acid medium and balancing in Basic medium. Sure, I know how to balance the equation but I want to know what it means physically. Why do we need to balance differently for different media? How is the medium related to the balancing of an equation? Can someone please throw some light on this?

 

[Borek]

To some extent there is no difference, it is just a matter of what is available in the solution (and sometimes of what is more convenient). When we balance reaction that occurs in a very low pH (like permanganate getting reduced to Mn(II)) it is more logical to balance hydrogen and oxygen using H⁺ and water:

MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O

than it would be to balance them with water and OH^- (even if technically it is possible:

MnO₄^- + 4H₂O + 5e^- → Mn²⁺ + 8OH^-

and the stoichiometry would be correct, just the reaction doesn't proceed like that).