Half equations

• Step one : Half equations

  Calculate the oxidation states on each side of the equation.

  E.G: VO^2+ -> VO2^+

  V +4 V +5

  BrO3^- -> Br2

  Br +5 Br 0
• Step Two: Half equations

  Balance the element changing oxidation state

  E.G: VO^2+ -> VO2^+

  V ALREADY BALANCED

  2BrO3^- -> Br2

  2 Br on the right so we need to add a 2 as left Br only has one.
• Step Three: Half Equations

  Sort out electrons.

  If oxidation state becomes more NEGATIVE from left to right then it GAINS electrons.

  If oxidation state becomes more POSITIVE from left to right then it LOOSES electrons

  VO^2+ -> VO2^+ +e-

  V's oxidation state becomes 1 more positive so one electron is lost.

  2BrO3^- +10e^- -> Br2

  Br becomes 5 more negative, however we've times it by 2 so 10 electrons are gained.
• Step Four: Half equations

  Balance Oxygens with H2O. For every O gained / lost, add or remove a H2O molecule.

  E.G: VO^2+ + H20 -> VO2^+ + e-

  1 less oxygen on the left so you have to balance it by adding H20 to the left also

  2BrO3 + 10e- -> Br2 + 6H20.

  6 more oxygens on left so need to add 6 H2Os to the right
• Step Five: Half equations

  Sort out Hydrogens. For every H gained or lost, add or remove one H+ molecules

  E.G: VO2+ H2O -> e- + 2H+

  2 Less H on the right so add two H+.

  2BrO^3- + 10e- + 12H+ -> Br2 + 6H20

  12 less H on the left so add 12 H+
• Step Six: Half equations

  Check if total charge on left equals total charge on right. If you're right it'll be the same
• Iodine Ions to iodine

  2I- -> I2 + 2e