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Halogens

Halogens. Physical Properties. Which Halogen is the best Oxidising Agent?. Potassium halide solutions Cl - (aq) Brl - (aq) l - (aq) Halogen dissolved in water Cl 2(aq), Br 2(aq) I 2(aq) Write brief plan of investigation Make predicted results table Write up results & conclusion.

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Halogens

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  1. Halogens

  2. Physical Properties

  3. Which Halogen is the best Oxidising Agent? • Potassium halide solutions • Cl-(aq) Brl-(aq) l-(aq) • Halogen dissolved in water • Cl2(aq), Br2(aq) I2(aq) • Write brief plan of investigation • Make predicted results table • Write up results & conclusion

  4. Displacement Reactions

  5. Chlorine displaces Br2 & I2 Cl2 + 2KBr → 2KCl + Br2 Cl2 is the oxidising agent Cl2 + 2Br- → 2Cl- + Br2 Cl2 + 2e- → 2Cl- Cl2 + 2KI → 2KCl + I2 Cl2 + 2I- → 2Cl- + I2

  6. Bromine displaces I2 Br2 + 2KI → 2KBr + I2 Br2 is the oxidising agent Br2 + 2I- → 2Br- + I2 Br2 + 2e- → 2Br-

  7. Halogens as Oxidising Agents Cl2 + 2Br- → 2Cl- + Br2 Cl2 + 2I- → 2Cl- + I2 Br2 + 2I- → 2Br- + I2 Cl2 Br2 I2 Strongest oxidising agent Oxidising Agents Accept Electrons-

  8. Halogens as Oxidising Agents Fluorine would displace all other halogens F2 + 2CI- → 2F- + Cl2 F2 > Cl2 > Br2 > I2 Increase in oxidising power Oxidising Agents Accept Electrons X2 + 2e-→ 2X-

  9. Halides as Reducing Agents The halide ions act as reducing agents 2X- → X2 + 2e- Reducing Agents Donate Electrons F- Cl- Br- I- Strongest reducing agent

  10. Which Halide is the best Reducing Agent? • Solid sodium halides • NaCl(s) NaBr(s) NaI(s) • Concentrated H2SO4 • Predictions • What products could be formed?

  11. Possible Products The halide ions act as reducing agents X- → X2 ? -1 0 The sulphuric acid acts as an oxidising agent H2SO4 → SO2 ? S ? H2S ? +4 0 +6 -2

  12. Results

  13. 1. Acid – Base Reactions • All halides can act as bases • Bases accept H+ ions NaX + H2SO4 → HX + NaHSO4 Base + acid → Hydrogen halide + salt NaF + H2SO4 → HF + NaHSO4 Hydrogen halide produced via acid-base reaction with ALL halides

  14. 2. Redox Reactions • Products of this stage depend on the reducing ability of the halide Reducing Agents Donate Electrons F- Cl- Br- I- Strongest reducing agent

  15. Sodium Bromide NaBr • Br-quite a good reducing agent H2SO4 → SO2 2H+ + 2e-+ H2SO4 → SO2 + 2H2O 2Br- →Br2 2Br- →Br2 + 2e- 2Br- + 2H+ + H2SO4 → SO2 + 2H2O + Br2

  16. Sodium Iodide NaI • I-very good reducing agent H2SO4 → SO2 2H+ + 2e-+ H2SO4 → SO2 + 2H2O 2I- →I2 2I- →I2 + 2e- 2I- + 2H+ + H2SO4 → SO2 + 2H2O + I2

  17. Sodium Iodide NaI • I-very good reducing agent H2SO4 → S 6H+ + 6e-+ H2SO4 → S+ 4H2O x 3 2I- →I2 + 2e- 6I- →3I2 + 6e- 6I- + 6H+ + H2SO4 → S+ 4H2O + 3I2

  18. Sodium Iodide NaI • I-very good reducing agent H2SO4 → H2S 8H+ + 8e-+ H2SO4 → H2S+ 4H2O x 4 2I- →I2 + 2e- 8I- →4I2 + 8e- 8I- + 8H+ + H2SO4 → H2S+ 4H2O + 4I2

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