Content Knowledge

• test for halides, I- , Br- , Cl-

  • add acidified silver nitrate solution
  • acidified using nitric acid to remove carbonate ions that may give other ppts
  • AgCl = white
  • AgBr = cream
  • AgI = yellow
• white, cream and yellow may look similar so a test using ammonia is used to distinguish between the halide ions
• test using ammonia

  • dilute ammonia is used followed by concentrated
  • if ppt dissolves in dilute = chloride
  • if ppt does not dissolve in dilute, but in conc = bromide
  • if ppt dissolves in neither = iodide
• bromide ions and conc sulfuric acid

  • H2SO4 + NaBr —> NaHSO4 + HBr
  • the acid oxides HBr which decomposes into H2 gas and Bromine, the acid itself is reduced to SO2
  • 2HBr + H2SO4 —> Br2 + SO2 + 2H2O
  • bromine is a reddish-brownish gas
• iodide ions with conc sulfuric acid

  • H2SO4 + NaI —> NaHSO4 + HI
  • HI decomposes readily
  • H2SO4 oxidises the HI, and is reduced to SO2
  • 2HI + H2SO4 —> I2 + SO2 + 2H2O
  • iodine is a purple/violet vapour
  • the conc acid oxides HI and is reduces to sulfur (yellow solid)
  • 6HI + H2SO4 —> 3I2 + S + 4H2O
• chloride ions and conc sulfuric acid;

  • conc acid is added dropwise to NaCl crystals to produce HCl gas
  • h2so4 + nacl —> nahso4 + hcl
  • hcl gas is seen as white fumes