2.7.2b: describe and carry out the following chemical reactions of halogens: (i) oxidation reactions with metal and nonmetallic elements and ions such as iron(II) and iron(III) ions in solution (ii) disproportionation reactions with cold and hot alkali, eg hot potassium hydroxide with iodine to produce potassium iodate(V)

OXIDATION REACTIONS

Halogens are oxidising agents

• oxidising power gets weaker down the group
• increased shielding
• increased atomic radius
• halogens can oxidise other halide ions

Halogens + metal

• Cl2(aq) + Fe2+(aq) → Fe3+(aq) + 2Cl-(aq)

Halogens + non-metal

• 5Cl2(g) + 2P(s) → 2PCl5(s)

DISPROPORTIONATION REACTIONS

Cl2(g) + H2O(l) ←> HCl(aq) + HOC(aq)

• Cl2 is oxidised to +1 in HOC and reduced to -1 in HCl

Halogens can react with cold, aqueous sodium hydroxide

• 2NaOH(aq) + Cl2(g) → NaCl(aq) + NaOCl(aq) + H2O(l)

Halogens can react with hot, concentrated potassium hydroxide

• 3I2(aq) + 6KOH(aq) → KIO3(aq) + 5KI(aq) + 3H2O(l)