To balance the oxygen and hydrogen for a redox reaction that takes place in acidic solution, it is necessary to use which of the following?A. H2O and H+

Question

B. H2O only
C. H2O and OH-
D. OH- only

Answer 1

I can tell you from many years of experience that MOST of the time the correct answer is A (H^+ and H2O) BUT that isn't always the correct answer.
For example, in the half reaction of
O2 ==> H2O we do the following:
first multiply H2O x 2.
O2 -->2H2O
O2 is zero, O in H2O is -2 for -4 total, add 4e to the left.
O2 + 4e ==>2H2O
Charge on left is -4, on right is zero, add 4H^+ to the left.
4H^+ + 4e + O2 --> 2H2O
Balanced by adding just H^+ and no water.