02. Ion Half Equation Rules

a) Getting charges to equal

Example:

Fe³⁺ → Fe²⁺ becomes Fe³⁺ + e^- → Fe²⁺

Cl₂ → 2Cl^- becomes Cl₂ + 2e^- → 2Cl^-

b) In respects to mass

Example:

SO₃^2- → SO₄^2- Extra oxygen atom needed

SO₃^2- + H₂O → SO₄^2- + 2H⁺ Protons on RHS as more hydrogen on LHS

SO₃^2- + H₂O → SO₄^2- + 2H⁺ + 2e^- Two electrons added as needs to balance in charge

c) Too much oxygen on one side

Example:

MnO₄^- + H⁺ → Mn²⁺ + 4H₂O Too much oxygen on LHS

MnO₄^- + 8H⁺ → Mn²⁺ + 4H₂O Four waters on RHS for the oxygens, but this needs hydrogens too so 8 on LHS

MnO₄^- + 8H⁺ + 5e^- → Mn²⁺ + 4H₂O Five electrons added to balance charge of manganate