Group 7 The Halogens

• Halogen displacement reactions:

  Cl2 +2KBr == Br2 + 2KCL

  Cl2+KI == I2 + KCl

  Br2 + KI == I2 +KBr

  For ionic equations remove spectator ions (K)
• Formation of Bleach

  2NaOH + Cl2 == NaClO+NaCl+H2O

  This is a disproportionation reaction

  Cl2 + H20 == HClO + HCl

  Benefits of using Cl outweigh the risk

  E.g. killing bacteria
• Reducing power increases going down the group

  Cl- = weakest

  Br - = middle

  I- = strongest
• Reactions with H2SO4:

  With Cl- Br - and I-

  NaCl + H2SO4 == NaHSO4 + HCl Observation = misty white fumes Swap with Br or I

  With Br - and I-

  NaBr + H2SO4 == Br2 +SO2 + 2H20 Observation = Brown fumes Swap with I

  With only I:

  6HI + SO2 == H2S + 3I2+2H20 Observation = Smell of rotten eggs
• Testing for Halides:

  Add nitric acid (HNO3) - removes any unwanted ions( Carbonate ions)

  Add Silver nitrate (AgNO3)

  Positive result =

  Cl- = White precipitate

  Br - = Cream precipitate

  I - = Yellow precipitate
• Further reaction with NH3:

  Cl- = dissolves in dilute NH3

  Br- = dissolves in conc NH3

  I- = does not dissolve