group 7: halogens

• how do the halogens appear at room temperature?

  fluorine – yellow gas

  chlorine – green gas

  bromine – dark red, volatile liquid, brown vapour

  iodine – shiny black solid, purple vapour
• how do the halogens appear in solution?

  fluorine – reacts with water

  chlorine – pale green

  bromine – orange/yellow

  iodine – brown
• why does the boiling point increase down group 7?

  1. size of molecule increases
  2. more Van Der Waals forces between molecules
  3. more energy needed to break intermolecular forces
• what type of agents are the halogen?

  oxidising agents
• what is the trend in oxidising power down group 7?

  decreases
• what is a displacement reaction?

  more reactive halogen displaces less reactive halogen from compound
• how is bromine extracted?

  from seawater by redox reaction
• how is iodine extracted?

  from kelp
• what is the test for the halide ions?

  1. add nitric acid
  2. add acidified silver nitrate
  3. add dilute ammonia and shake
  4. add concentrated ammonia
• which halide ion will not give a positive result with any test?

  fluoride ion
• why is nitric acid added?

  to remove any carbonate or hydroxide ions
• what is the positive result for chloride ions?

  acidified silver nitrate – white precipitate

  dilute ammonia – precipitate dissolves

  concentrated ammonia – n/a
• what is the positive result for bromide ions?

  acidified silver nitrate – cream precipitate

  dilute ammonia – precipitate remains

  concentrated ammonia – precipitate dissolves
• what is the positive result for iodide ions?

  acidified silver nitrate – yellow precipitate

  dilute ammonia – precipitate remains

  concentrated ammonia – precipitate remains
• why does the reducing power increase down group 7?

  1. acid base reaction
  2. reduction of sulphuric acid
• what are the products of acid base reaction?

  HX + NaHSO4
• what are the products of reduction of sulphuric acid reaction?

  Bromine – X2 + H2O + SO2

  iodine – X2 + H2O + SO2 + S + H2S
• what are the observations of NaF reaction?

  white misty fumes – HF
• what are the observations of NaCl reaction?

  white misty fumes – HCL
• what are the observations of NaBr reaction?

  white misty fumes – HBr

  brown vapour – Br2

  colourless choking gas – SO2
• what are the observations of NaI reaction?

  white misty fumes – HI

  purple vapour – I2

  colourless choking gas – SO2

  yellow solid – S

  bad smell – H2S
• how are chlorine and water used in water treatment?

  chloric (1) acid is oxidising agent and kills bacteria
• what is the equation for chlorine and water being used in water treatment?

  Cl2+ H2O <--> HC + HClO
• what is the test for chlorine and water being used in water treatment?

  litmus paper

  red – HCl

  white – HClO
• how can chlorine gas be used in water if it is toxic?

  health benefit benefits outweigh the toxicity

  it's used in small concentrations
• what is produced when chlorine and water react in sunlight?

  hydrogen chloride and oxygen
• what is the equation for chlorine and water reacting in sunlight?

  2Cl2 + 2H2O --> 4HCl + O2
• what is the equation for the reaction of chlorine and sodium hydroxide?

  Cl2 + 2NaOH --> NaCl + NaClO + H2O
• what are the conditions for the reaction between chlorine and sodium hydroxide?

  sodium hydroxide must be cold, dilute and aqueous
• what are the uses of chlorine?

  1. water treatment
  2. extraction of titanium
  3. bleaches
  4. weed killers and pesticides
  5. dyes and pharmaceuticals