Answer:
How about this?
Explanation:
The following ideas might get you started. This is a practical, so I leave the experimental details to you.
1) Reduction of dichromate ion
Slow addition of 5 % hydrogen peroxide to an acidic solution of potassium dichromate.
The skeleton equation is
1×[Cr₂O₇²⁻ + 14H⁺ + 6e⁻ ⟶ 2Cr³⁺ + 7H₂O]
3×[H₂O₂ ⟶ O₂ + 2H⁺ + 2e⁻]
Cr₂O₇²⁻ + 3H₂O₂ + 8H⁺ ⟶ 2Cr³⁺ + 3O₂ + 7H₂O
orange colourless blue-green colourless gas
2) Reduction of permanganate ion
Slow addition of an acidic potassium permanganate solution to a solution of iron(II) chloride.
The equations are
2×[MnO₄⁻ + 8H⁺ + 5e⁻ ⟶ Mn²⁺ + 4H₂O]
5×[Fe²⁺⟶ Fe³⁺ + e⁻]
2MnO₄⁻ + 5Fe²⁺ + 16H⁺ ⟶ 2Mn²⁺ + 5Fe³⁺ + 8H₂O
deep purple pale green pale orange-pink yellow-brown
3) Reduction of vanadium(V) to vanadium(II)
Addition of an acidic solution of ammonium metavanadate to granular zinc. There are various colour changes as the vanadium is reduced by the zinc from V(V) ⟶ V(IV) ⟶ V(III) ⟶ V(II).
The equations are
2×[VO₂⁺ + 2H⁺ + e⁻ ⟶ VO²⁺ + H₂O]
1×[Zn ⟶ Zn²⁺ + 2e⁻]
2VO₂⁺ + Zn + 4H⁺ ⟶ 2VO²⁺ + Zn²⁺ + 2H₂O
yellow blue
2×[VO²⁺ + 2H⁺ + e⁻ ⟶ V³⁺ + H₂O]
1×[Zn ⟶ Zn²⁺ + 2e⁻]
2VO²⁺ + Zn + 4H⁺ ⟶ 2V³⁺ + Zn²⁺ + 2H₂O
blue green
2×[V³⁺ + e⁻ ⟶ V²⁺]
1×[Zn ⟶ Zn²⁺ + 2e⁻]
2V³⁺ + Zn ⟶ 2V²⁺ + Zn²⁺
green lilac
