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Halogens: F 2 , Cl 2 , Br 2 , I 2

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 - ). The oxidising power reduces as you move down Group 17 F 2 < Cl 2 < Br 2 < I 2. Strongest oxidant – greatest electron pulling power.

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Halogens: F 2 , Cl 2 , Br 2 , I 2

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  1. Halogens: F2, Cl2, Br2, I2 • Halogens as oxidants: • Halogens attract electrons from other substances – they are all oxidants (they nick e-) 12 Chemistry 2.2 quantitative chemistry CR 07

  2. The oxidising power reduces as you move down Group 17 • F2 < Cl2 < Br2 < I2 Strongest oxidant – greatest electron pulling power Weakest oxidant 12 Chemistry 2.2 quantitative chemistry CR 07

  3. 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 12 Chemistry 2.2 quantitative chemistry CR 07

  4. F2 < Cl2 < Br2 < I2 • If chlorine gas is bubbled through seawater bromine is liberated: • 2KBr(aq) + Cl2(g) 2KCl(aq) + Br2(aq) • Ionic equation: • 2Br-(aq) + Cl2(g) 2Cl-(aq) + Br2(aq) • Cl2 has oxidised Br- to Br2 12 Chemistry 2.2 quantitative chemistry CR 07

  5. Halogens and hydrogen • Halogens oxidise hydrogen to form halides. Hydrogen halides are acidic in water • eg. H2(g) + Cl2(g)  2HCl(g) 12 Chemistry 2.2 quantitative chemistry CR 07

  6. Halogens and metals • Halogens oxidise metals to form metal halides. • eg. 2Na(s) + Cl2(g)  2NaCl(s) • 2Al(g) + 3Cl2(g)  2AlCl3(g) 12 Chemistry 2.2 quantitative chemistry CR 07

  7. Halogens and water • Fluorine, (the strongest oxidant), reacts immediately with water. It oxidises the oxide ion (O2-) to form an acid and release oxygen gas. • 2F2(g) + 2H2O (l)  4HF(aq) + O2(g) • Hydrofluoric acid 12 Chemistry 2.2 quantitative chemistry CR 07

  8. Chlorine and water • Chlorine forms 2 acids with water: • Cl2(g) + H2O (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 12 Chemistry 2.2 quantitative chemistry CR 07

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

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

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