1. Permanganate reactions

2. Manganese exists in many different oxidation states, each with a characteristic colour including: Mn VII: MnO 4 – purple Mn VI: MnO 4 2– deep green Mn IV MnO 2 dark brown Mn 2+ Mn 2+ colourless or very pale pink The many states of manganese

3. Fresh hydrogen peroxide solution is acidified with sulfuric acid. We don’t use HCl because the Cl - ion can act as a reducing agent. Permanganate in acid conditions

4. Purple permanganate solution turns colourless as it is added to the acidified peroxide. The MnO 4 – /H + has been reduced to Mn 2+.

5. Oxygen gas is again produced, but is not visible in this very dilute solution. MnO 4 - + 8H + + 5e - → Mn 2+ + 4H 2 O H 2 O 2 → O 2 + 2H + + 2e - 5H 2 O 2 + 2MnO 4 - + 6H + → 5O 2 + 2Mn 2+ + 8H 2 O

6. Hydrogen peroxide is neutral. Permanganate in neutral conditions

7. When potassium permanganate solution is added, the purple solution turns brown. The MnO 4 – has been reduced to MnO 2 is formed.

8. If you look closely, you can see bubbles of a colourless gas being formed.

9. Leave the beaker to settle for 10 minutes and a brown solid is clearly visible.

10. Neutral permanganate is reduced to MnO 2 (s): MnO 4 - + 4H + + 3e - → MnO 2 (s) + 2H 2 O purple brown H 2 O 2 → O 2 (g) + 2H + + 2e - 2MnO 4 - + 2H + + 3H 2 O 2 → 2MnO 2 + 4H 2 O + 3O 2

11. In the HSO 3 - ion, sulfur is in the +4 oxidation state. Sodium hydrogen sulfite is a white solid which dissolves in water to form a colourless solution. Permanganate in alkaline conditions

12. Sodium hydroxide solution is added to make the solution alkaline.

13. Purple potassium permanganate solution is added. The purple solution turns green.

14. MnO 4 - + e - → MnO 4 2-

15. The green solution turns brown, then orange, and finally colourless as the excess HSO 3 - further reduces the green MnO 4 2- to brown MnO 2 and then colourless Mn 2+. The alkaline solution is acidified by adding hydrochloric acid.

16. Finally we add barium chloride solution, which reacts to form a white precipitate. This confirms that the HSO 3 - has been oxidised to SO 4 2-. The solution had to be acidified first, because Ba(OH) 2 is only slightly soluble.

17. MnO 4 - + e - → MnO 4 2- purple green HSO 3 - + H 2 O → SO 4 2- + 3H + + 2e - 2MnO 4 - + HSO 3 - + H 2 O → 2MnO 4 2- + SO 4 2- + 3H +

18. In acidic conditions, purple MnO 4 – is reduced to colourless Mn 2 +(aq): 5H 2 O 2 + 2MnO 4 - + 6H + → 5O 2 + 2Mn 2+ + 8H 2 O In neutral conditions, purple MnO 4 – is reduced to dark brown MnO 2 (s): 2MnO 4 - + 2H + + 3H 2 O 2 → 2MnO 2 + 4H 2 O + 3O 2 In alkaline conditions, purple MnO 4 – is reduced to dark green MnO 4 2– (aq) : 2MnO 4 - + HSO 3 - + H 2 O → 2MnO 4 2- + SO 4 2- + 3H + Summary