halogens

• sodium bromide + sulphuric acid makes misty fumes (HBr), choking fumes (SO2), and brown fumes (Br2)
• sodium fluoride/chloride + sulphuric acid makes misty fumes (HF or HCl)
• sodium iodide + sulphuric acid makes misty fumes (HI), choking fumes (SO2), grey solid (I2), and toxic bad egg smell (H2S)
• the reducing power (ability to oxidise) increases down the halogens
• in the test for halides, the nitric acid removes unwanted ions (namely carbonate ions)
• in the test for halides, the precipitate goes more yellow down the halogens
• the oxidating power (ability to reduce) decreases down the halogens
• silver chloride easily dissolves in dilute ammonia solution
• silver bromide dissolves only in concentrated ammonia solution
• silver iodide will not dissolve in any ammonia solution
• a hydrogen halide produces steamy fumes
• bromine produces brown fumes
• iodine is a black / grey solid that produces purple fumes
• hydrogen sulphide produces a rotten egg smell
• silver fluoride produces no precipitate
• HClO is chloric (I) acid. It is a mild oxidising agent. It is effective at killing bacteria without being harmful to humans. For this reason, a small amount of chlorine dissolved in water will sterilise the water and so chlorine is widely used in swimming pools and in water treatment for this reason.
• chlorine disproportionates with water and dilute alkalis
• sulphur dioxide produces choking fumes
• Reaction of sodium iodide with concentrated sulphuric acid

  NaI + H2SO4 -> HI + NaHSO4

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

  6 HI + H2SO4 -> 3 I2 + S + 4 H2O

  8 HI + H2SO4 -> 4 I2 + H2S + 4 H2O