Group 7

• oxidising agents accept electrons, oxidising ability decreases down the group
• halides show increasing reducing power down the group, they donate electrons more easily
• F- and Cl- ions are not strong enough to reduce the sulfur in H2SO4, so there is no redox reaction, only an acid-base reaction
• Br- and H2SO4

  • acid-base reaction take place, then Br- reduces sulphuric acid to SO2
  • the acid reacts as a proton donator in the first reaction, and then an oxidising agent in the second
  • reduction product= so2
  • observations ; white fumes (HBr), Orange fumes (Br2) and colourless acidic gas (SO2)
• I- ions

  • the strongest reducing agent, can reduce sulfur from +6 in sulfuric acid, to +4 in SO2, to 0 in Sulfur and -2 in H2S
  • there are 3 redox steps (H2SO4 to SO2, S, then H2S)
  • observations; white fumes (HI) , purple fumes and black solid (I2), colourless acidic gas ( SO2) , yellow solid (S) and a gas with a bad smell of eggs (H2S)
• Appearances

  • F2 = very pale yellow gas, highly reactive
  • Cl2= greenish, reactive gas, poisonous in high concentrations
  • Br2= a red liquid, gives of orange poisonous fumes
  • I2= shiny grey solid, gives off purple gas when reacts
• Ammonia + AgX

  • AgCl= dissolves in dilute ammonia
  • AgBr= dissolves in CONCENTRATED ammonia
  • AgI= too insoluble, dissolves in neither