12 Chemistry 2.2 quantitative chemistry CR 07

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

The oxidising power reduces as you move down Group 17

F2 < Cl2 < Br2 < I2Weakest oxidant

Strongest oxidant – greatest electron

pulling power

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

12 Chemistry 2.2 quantitative chemistry CR 07

F2 < Cl2 < Br2 < I2If 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

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

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

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

Chlorine and waterChlorine 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

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

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