Halogens 6.3
6.3 Halogens & Halides
When
chlorine solution mixes with
KBr solution a reaction occurs:
Cl2(aq) + 2Br-(aq) → 2Cl-(aq) + Br2(aq) (
Yellow/
Orange)
The chlorine has
oxidised the bromide ions (removed their electrons) and therefore
reduced itself. The electron half-equations are therefore:
2Br-(aq) → Br2(aq) + 2e- and
Cl2(aq) + 2e- → 2Cl-(aq).
Reacting Br
2 with Cl
- gives
no reaction (as Bromine is not a powerful enough oxidising agent to take electrons from Cl ions). This is part of a trend.
For a reaction to occur the halogen must be more powerful (i.e. higher in group) than the halide ion it is trying to remove electrons from.
Iodine is Yellow/Brown and is confusable with Bromine adding a
HC solvent distinguishes: Iodine →
Purple and Bromine →
Brown/
Orange