Group 7

• electronegativity decreases as you go down the group
• melting point increases as you go down the group
• oxidising ability decreases down the group
• Cl2 displaces Br- and I-

  Br2 displaces I-

  I2 doesnt displace
• Reducing power increases going down the gorup
• Reaction of H2SO4 with NaF, NaCl or NaBr (X)

  NaX + H2SO4 -> NaHSO4 + HX
• Reaction of NaBr with H2SO4 (2 stages)

  NaBr + H2SO4 -> NaHSO4 + HBr

  2 HBr + H2SO4 -> Br2 + SO2 + 2 H2O
• reaction of NaI with H2SO4 (3 stages)


  NaI + H2SO4 -> NaHSO4 + HI

  2 HI + H2SO4 -> I2 + SO2 + 2 H2O

  6 HI + SO2 -> H2S + 3 I2 + 2 H2O
• Test for halides:


  + dilute HNO3 to remove impurities

  + AgNO3 (aq)

  -> Cl- = white ppt

  -> Br- = cream ppt

  -> I- = yellow ppt

  + dilute NH3 -> AgCl dissolves

  + conc NH3 -> AgBr dissolves
• What do you add in the test for halides?


  HNO3 then AgNO3 then NH3
• What silver halide dissolves in dilute NH3?


  AgCl
• What silver halide dissolves in concentrated NH3?


  AgBr
• Which halide forms a yellow precipitate with AgNO3?


  iodine
• what reactions do chlorine undergo with water?


  disproportionation
• Chlorine with water:

  Cl2 (g) + H2O (l) -> HCl (aq) + HClO (aq) -> 2 H+ + ClO- + Cl-
• Chlorine with water in sunlight:


  2 Cl2 (g) + 2 H2O (l) -> 4 HCl (aq) + O2(g)
• What is chlorine used for?


  to treat water
• what are the risks of using chlorine in water treatment?


  • irritates the respiratory system in inhaled
  • can cause chemical burns
  • forms chloromethate which can react with organic compounds in water to become a carconagentic
• Chlorine and clod NaOH:


  Cl2 (aq) + 2 NaOH (aq) -> NaCl (aq) + NaClO (aq) + H2O (l)
• what is the solution of NaCl and NaClO used for?


  as bleach