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In the half-reaction method, how are oxygen atoms balanced?
ABy adding O2 molecules where needed
BBy adding hydroxide ions to one side
CBy adding water molecules where needed
DBy adding electrons to the deficient side
Answer & Solution
Correct answer: C. By adding water molecules where needed
1. Write the two half-reactions and balance every element apart from oxygen and hydrogen first.
2. Oxygen is then balanced by adding water molecules to the side that is short of oxygen.
3. Hydrogen is balanced next by adding hydrogen ions.
4. Electrons come last, and they balance charge rather than atoms.
5. Adding O2 is never part of the method, since the medium supplies oxygen as water.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.2 Classifying Chemical Reactions_
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