halide salts with concentrated sulfuric acid

• A reducing agent donates electrons - looses electrons itself

  • The reducing power of the halides increases down group 7 because as the ions get bigger it is easier for the outer electrons to be given away as the attraction from the nucleus on them becomes weaker
• NaF and NaCl :

  F- and Cl- ions are not strong enough reducing agents to reduce the S in H2SO4 . No redox reactions occur only acid-base reactions occur

  • oxidation states of halide and sulfur stay the same (-1 and +6)
• Reactions of NaF and NaCl with H2SO4:

  • NaF(s) + H2SO4 (l) ----> NaHSO4 (s) + HF(g)
  • NaCl(s) + H2SO4 (l) ----> NaHSO4 (s) + HCl(g)

  OBSERVATIONS:

  White misty fumes of HF and HCl are evolved
• NaBr:

  Br- ions are stronger reducing agents than Cl- and F- and after the initial acid-base reaction, the bromide ions reduce the sulfur in H2SO4 from +6 to + 4 in SO2

  • acid base reaction
  • REDOX REACTION where sulfur is reduced
• Reactions of NaBr with H2SO4:

  1. NaBr(s) + H2SO4 (l) ----> NaHSO4 (s) + HBr(g)
  2. 2H+ + 2Br- + H2SO4 (l) ----> Br2 (g) + SO2 (g) + 2 H2O(l)

  OBSERVATIONS:

  (acid base reaction) white misty fumes of HBr gas

  (REDOX reaction) choking fumes of SO2 and orange fumes of Br2
• NaI:

  I- ions are the strongest halide reducing agents. They can reduce the sulfur from...

  • +6 in H2SO4 to + 4 in SO2
  • +4 in SO2 to -2 in H2S
• Reactions of NaI with H2SO4:

  1. NaI(s) + H2SO4 (l) ----> NaHSO4 (s) + HI(g)
  2. 2H+ + 2I- (g)+ H2SO4 (l) ----> I2 (s) + SO2 (g) + 2 H2O(l)
  3. 6H+ + 6I- (g) + H2SO4 (g) ----> S (s) + 3I2 (s) + 4H2O (l)
  4. 8H+ + 8I- (g) + H2SO4 (g) ----> H2S (g) + 4I2 (s) + 4H2O (l)

  OBSERVATIONS

  (acid base reaction) white misty fumes of HI

  (REDOX reaction) choking fumes of SO2 and black solid of iodine with purple fumes

  (REDOX reaction) H2S eggy smelling fumes and black solid iodine