2 Displacement of halide by halogen

1. The displacement reactions of halide ions by halogens. A halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds The oxidising strength decreases down the group. Oxidising agents are electron acceptors. Chlorine will displace both bromide and iodide ions; bromine will displace iodide ions Chlorine (aq) Bromine (aq) Iodine (aq) potassium chloride (aq) Very pale green solution, no reaction Yellow solution, no reaction Brown solution, no reaction potassium bromide (aq) Yellow solution, Cl has displaced Br Yellow solution, no reaction Brown solution, no reaction potassium iodide (aq) Brown solution, Cl has displaced I Brown Solution, Br has displaced I Brown Solution, no reaction The colour of the solution in the test tube shows which free halogen is present in solution. Chlorine =very pale green solution (often colourless), Bromine = yellow solution Iodine = brown solution (sometimes black solid present) know these observations ! Cl2 (aq) + 2Br – (aq)
2Cl – (aq) + Br2 (aq) Cl2 (aq) + 2I – (aq)
2Cl – (aq) + I2 (aq) Br2 (aq) + 2I – (aq)
2Br – (aq) + I2 (aq) be able to write these reactions as two half equations showing oxidation or reduction e.g. 2Br – (aq)
Br2 (aq)+ 2eCl2 (aq)+ 2e-
2Cl- (aq)