• The reactivity of halogens is also shown by their?displacement?reactions?with other halide ions in solutions
• A?more?reactive?halogen can displace a?less reactive?halogen from a halide solution of the less reactive halogen
• Eg. The addition of chlorine water to a solution of bromine water:

Cl2?(aq) + 2NaBr (aq) → 2NaCl (aq) + Br2?(aq)

• The chlorine has displaced the bromine from solution as it is more reactive which can be summarised in the following ionic equation:

Cl2?(aq) + 2Br-?(aq) → 2Cl-?(aq) + Br2?(aq)

Chlorine with Bromides & Iodides

• If you add chlorine solution to colourless potassium bromide or potassium iodide solution a displacement reaction occurs:
  • The solution becomes?yellow-orange?as bromine is formed
  • The solution becomes?brown?as iodine is formed

   

• If an?organic solvent?is added, such as cyclohexane, the following observations are seen:
  • The organic layer will appear?yellow-orange?as bromine is formed
  • The organic layer will appear?purple?as iodine is formed
  • The organic solvent is useful as the the halogens are more soluble in this layer which helps observe the colour changes more easily
• Chlorine is?above?bromine and iodine in Group 7 so it is more reactive
• Chlorine will?displace?bromine or iodine from an aqueous solution of the metal halide:

Cl2?(aq) + 2KBr (aq) →?2KCl (aq) + Br2?(aq)

chlorine + potassium bromide?→??potassium chloride + bromine

Cl2?(aq) + 2KI (aq) →?2KCl (aq) + I2?(aq)

chlorine + potassium iodide?→??potassium chloride + iodine

Bromine with Iodides

• Bromine is above iodine in Group 7 so it is?more?reactive
• Bromine will displace iodine from an aqueous solution of the metal iodide

bromine + potassium iodide?→??potassium bromide + iodine

Br2?(aq) + 2KI (aq) → 2KBr (aq) + I2?(aq)

• The reaction will turn?brown?as iodine is formed
• If an organic solvent is added the organic layer will appear?purple?as iodine is formed