1. 12 Chemistry 2.2 quantitative chemistry CR 07 Halogens: F 2, Cl 2, Br 2, I 2 Halogens as oxidants: Halogens attract electrons from other substances – they are all oxidants (they nick e - )

2. 12 Chemistry 2.2 quantitative chemistry CR 07 The oxidising power reduces as you move down Group 17 F 2 < Cl 2 < Br 2 < I 2 Weakest oxidant Strongest oxidant – greatest electron pulling power

3. 12 Chemistry 2.2 quantitative chemistry CR 07 Reacting with halides Fluorine is the most powerful oxidant and will oxidise other halides. Chlorine can oxidise bromide and iodide. Bromine can only oxidise iodide

4. 12 Chemistry 2.2 quantitative chemistry CR 07 F 2 < Cl 2 < Br 2 < I 2 If chlorine gas is bubbled through seawater bromine is liberated: 2KBr (aq) + Cl 2(g) 2KCl (aq) + Br 2(aq) Ionic equation: 2Br - (aq) + Cl 2(g) 2Cl - (aq) + Br 2(aq) Cl 2 has oxidised Br - to Br 2

5. 12 Chemistry 2.2 quantitative chemistry CR 07 Halogens and hydrogen Halogens oxidise hydrogen to form halides. Hydrogen halides are acidic in water eg. H 2(g) + Cl 2(g) 2HCl (g)

6. 12 Chemistry 2.2 quantitative chemistry CR 07 Halogens and metals Halogens oxidise metals to form metal halides. eg. 2Na (s) + Cl 2(g) 2NaCl (s) 2Al (g) + 3Cl 2(g) 2AlCl 3(g)

7. 12 Chemistry 2.2 quantitative chemistry CR 07 Halogens and water Fluorine, (the strongest oxidant), reacts immediately with water. It oxidises the oxide ion (O 2- ) to form an acid and release oxygen gas. 2F 2(g) + 2H 2 O (l) 4HF (aq) + O 2(g) Hydrofluoric acid

8. 12 Chemistry 2.2 quantitative chemistry CR 07 Chlorine and water Chlorine forms 2 acids with water: Cl 2(g) + H 2 O (l) HCl (aq) + HOCl (aq) Hydrochloric acid and hypochlorous acid The mixture is known as chlorine water The HOCl dissociates and the OCl - ion reacts with Na + to form NaOCl – sodium hyperchlorite

9. 12 Chemistry 2.2 quantitative chemistry CR 07 NaOCl – sodium hyperchlorite - is used for bleaching which is oxidation of stains. Strong solutions cause burns because it is a powerful oxidising agent.

10. 12 Chemistry 2.2 quantitative chemistry CR 07 Household bleach Household bleach contains OCl - ions which destroy dyes by oxidising them to colourless products. Why NaOCl? HOCl is too unstable to be isolated in pure form