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Is there an easier way or clear set rule in determining which side of the reaction to put the H20 or the OH- or is it determined purely through trial and error? Is it different or the same as compared to an acidic solution?
In both acidic and basic solutions for redox reactions, you start with balancing the core element, and then move on to balancing the number of oxygens by adding H2O. Balancing the hydrogens after this is where the two differ: in acidic solutions, you simply add H+ to the side that needs more hydrogens. In basic solutions, however, you will add the number of H2O molecules that is the same number as the amount of hydrogens you need to balance the rxn. You will add this same number of OH- to the opposite side of the rxn to make sure there is a net gain of hydrogens; if I need 6 hydrogens on the reactants' side to balance the rxn, I will add 6 molecules of H2O to the reactants' side, and 6OH- to the products' side. Make sure you also balance the charges of the reactants and products with the right number of electrons at the end!
I always start with balancing with H20 and then move on to OH- or H+. Makes it easier for me. The one that you use depends on the type of solution you are in, and balance other parts of the reaction before you start adding hydrogens and oxygens.
An alternative way to balance redox reactions in basic solutions is just to balance it like you would for an acidic solution, then add OH- for every H+ there is on both sides of the equation, and then use H+ + OH- -> H2O so that there are only OH- and H2O molecules in the final balanced equation.
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