Qualitative analysis + Halogens

• What is the trend in carbon to halogen bond enthalpies?

  They decrease from chlorine to bromine to iodine since carbon to chlorine is the highest
• What is the reagent for the ammonium ion test?

  Heating with NaOH but not ammonia
• What is the reagent for the sulfate ion test?

  BaCl2 or Ba(NO3)2
• What is the reagent for the halide ion test?

  AgNO3 + dilute HNO3
• What is the reagent for the carbonate ion test?

  HNO3
• What is a positive result for the carbonate test?

  Effervescence
• What is a positive result for the sulfate ion test?

  White precipitate
• What is a positive result for the ammonium ion test?

  Indicator paper turns blue
• What is a positive result for chloride, bromide and iodide ions?

  White, cream, yellow precipitates
• Why do boiling points increase down group 7?

  More London forces as the atoms are bigger
• Why does electronegativity decrease down group 7?

  Positive nucleus further from bonding electrons since atoms are bigger, more sheilding
• What do you add to halide displacement reactions and why?

  An organic solvent like Hexane, halogens dissolves and forms a layer on top of the aqueous layer, easier to observe colour change
• When chlorine ions displace bromine ions what colours are the layers?

  Aq: Yellow, Org: orange
• When chlorine ions displace iodine ions what are the colours of the layers?

  Aq: brown, Org: purple
• When bromine ions displace iodine ions what are the colours of the layers?

  Aq: brown, Org: purple
• When iodine ions are added to a solution with more reactive halide ions what are the colours of the layers?

  Aq: brown, Org: purple
• When bromine ions are added to a solution with more reactive halide ions what are the colours changes?

  Aq: yellow Org: orange
• When chlorine ions are added to a solution with other chlorine ions what will be the colour of the layers?

  Colourless
• what does the white precipitate dissolve in?

  dilute ammonia
• What does the cream precipitate dissolve in?

  Concentrated ammonia
• What does the yellow precipitate dissolve in?

  Is insoluble in concentrated ammonia
• What is a disproportionation reaction?

  Something gets oxidised and reduced
• What is sodium chlorate(l) and what is it used for?

  treating water, bleaching paper and fabrics, cleaning agents (bleach)
• Why is adding chlorine to water important?

  ClO- chlorate(l) ions form and are used for killing bacteria, drinking water or pools
• chloric(l) acid ionises into chlorate(l) ions

  HClO + H2O -> ClO- + H3O+
• What are the advantages of chlorinating drinking water?

  Destroys microorganisms, long lasting so reduces bacteria buildup further down the supply, reduces algae growth which gives water a bad smell and taste
• What are disadvantages of chlorinating drinking water?

  Gas is toxic and irritates respiratory system, liquid chlorine causes severe chemical burns to skin, can react with organic compounds to make cancer causing chloroalkanes but if we didn’t have it there is a risk of cholera
• What is an ethical consideration of chlorinating water?

  It is done all over the UK and we have no choice
• Why is ozone an alternative to chlorinating drinking water? flaws?

  Kills microorganisms but has a short half life and is expensive
• Why is UV an alternative to chlorinating drinking water? Flaws?

  Damages DNA in microorganisms, ineffective in cloudy water, doesn’t prevent water being contaminated further down the process
• How do you test for ammonium ions?

  Add sodium hydroxide, gently heat, hold up red litmus paper, if it turns blue it has ammonium ions
• How do you test for hydroxides?

  If litmus paper turns blue its alkaline, further testing must be done as it could be any alkali
• What can you do after the carbonate test to make sure you have carbonate ions?

  Bubble it through limewater to see if it turns cloudy
• What is the chemical equation for the ammonium ion test?

  NH4+ + OH- -> NH3 + H2O
• Why can aqueous compounds conduct electricity?

  Ions are mobile
• What is the ionic equation for bromine ions displacing iodine ions?

  Br2 + 2I- -> 2Br- + I2
• What is the name of NaBrO3?

  Sodium bromate (V)
• BrO-

  bromate (l)
• BrO2-

  bromate (ll)
• BrO3-

  Bromate (lll)