Question

Water is used to balance O atoms in the half-reaction method. Why can’t${\mathbf{O}}^{\mathbf{2}\mathbf{-}}$ions be used instead?

Short answer

Because water is an electrically neutral molecule, it is employed to balance oxygen atoms in the half-cell reaction method.

Step-by-step solution

What is the half-reaction method

We split the supplied reaction into two half-reactions using the half-reaction approach. To achieve the total response, we balance the two half-reactions separately and combine them.

Determining why can’t O2- ions be used instead 

Water is a positively charged ion, whereas ${\mathrm{O}}^{2-}$is an electrically neutral molecule.

The act of balancing a reaction entails balancing both the atoms and the charge. If a charged ion, such as ${\mathrm{O}}^{2-}$, is employed, only the atoms will be balanced, leaving the charge imbalanced.

As a result, in the half-cell reaction method, water is required to balance oxygen