How to balance this rxn?

Question

using half-reaction method to balance this acidic reaction:

Zn As2O3→AsH3

Thank you very much! X(

Answer 1

Steps as follows ...

As2O3 -->  2AsH3

oxygens in reactant form water molecules. So

As2O3  -->  2AsH3 + 3H2O

Now provide necessary hydrogens by H+.  So

As2O3 +12H+  -->  2AsH3 + 3H2O

Now provide electrons to produce 'balanced charges'.  So final equn is.

As2O3 +12H+ + 12e -->  2AsH3 + 3H2O

Zn -->  Zn2+ + 2e (need to multiply this by 6 before adding so electrons cancel)

So ...

As2O3 + 6Zn + 12H+ --> 2AsH3 + 6Zn2+ + 3H2O

OK?