Halogens

• What is the physical state and color of fluorine (F2)?


  Very pale yellow gas
• What is the physical state and color of chlorine (Cl2)?


  Greenish, reactive gas
• What is the physical state and color of bromine (Br2)?


  Red liquid that gives off dense brown/orange poisonous fumes
• What is the physical state and color of iodine (I2)?


  Shiny grey solid that sublimes to purple gas
• What is the trend in melting and boiling points of halogens down the group?


  • Melting and boiling points increase down the group
  • Larger molecules have more electrons
  • Larger van der Waals forces require more energy to break
• What is the trend in electronegativity of halogens down the group?


  • Electronegativity decreases down the group
  • Atomic radii increase due to more shells
  • Nucleus is less able to attract bonding electrons
• What is the relationship between oxidizing strength and halogens?


  • Stronger oxidizing agents displace weaker ones
  • Oxidizing strength decreases down the group
  • Chlorine displaces bromide and iodide ions
• What color solution indicates the presence of chlorine in a reaction?


  Very pale green solution (often colorless)
• What color solution indicates the presence of bromine in a reaction?


  Yellow solution
• What color solution indicates the presence of iodine in a reaction?


  Brown solution (sometimes black solid present)
• What are the half-equations for the displacement reactions of halide ions by halogens?


  • For bromide: $2Br^- \rightarrow Br_2 +$$2e^-$
  • For chlorine: $Cl_2 +$$2e^- \rightarrow 2Cl^-$
• What is the test for halide ions using silver nitrate?


  • Acidify with nitric acid
  • Add silver nitrate dropwise
  • Fluorides: no precipitate
  • Chlorides: white precipitate
  • Bromides: cream precipitate
  • Iodides: pale yellow precipitate
• What is the reaction of chlorides with silver nitrate?


  Produces a white precipitate of AgCl(s)
• What is the reaction of bromides with silver nitrate?


  Produces a cream precipitate of AgBr(s)
• What is the reaction of iodides with silver nitrate?


  Produces a pale yellow precipitate of AgI(s)
• How can silver halide precipitates be differentiated?


  • Silver chloride dissolves in dilute ammonia
  • Silver bromide dissolves in concentrated ammonia
  • Silver iodide does not react with ammonia
• What is the reaction of halide salts with concentrated sulfuric acid?


  • F- and Cl-: acid-base reactions only
  • Br-: reduces sulfur from +6 to +4
  • I-: strongest reducing agent, reduces sulfur to +4, 0, and -2
• What is the observation when NaF reacts with concentrated sulfuric acid?


  White steamy fumes of HF are evolved
• What is the observation when NaCl reacts with concentrated sulfuric acid?


  White steamy fumes of HCl are evolved
• What is the observation when NaBr reacts with concentrated sulfuric acid?


  White steamy fumes of HBr and orange fumes of bromine are evolved
• What is the observation when NaI reacts with concentrated sulfuric acid?


  White steamy fumes of HI, black solid of iodine, and purple fumes of iodine are evolved
• What is disproportionation in the context of chlorine reactions?


  • Chlorine simultaneously oxidizes and reduces
  • Example: $Cl_2 +$$H_2O \rightleftharpoons HClO +$$HCl$
• What happens when chlorine reacts with water in sunlight?


  • Reaction: $2Cl_2 +$$2H_2O \rightarrow 4H^+$$+$$4Cl^- +$$O_2$
  • Greenish color fades, colorless gas (O2) produced
• What is the reaction of chlorine with cold dilute NaOH solution?


  • Reaction: $Cl_2 +$$2NaOH \rightarrow NaCl +$$NaClO +$$H_2O$
  • Used as bleach and disinfectant
• What ions are tested for using silver nitrate solution?

  Fluoride, chloride, bromide, iodide
• Why must the solution be acidified with dilute nitric acid?

  To remove other ions that cause confusion
• What is the observation for chloride ions when tested with silver nitrate?

  White precipitate
• What is the observation for bromide ions when tested with silver nitrate?

  Very pale cream precipitate
• What is the observation for iodide ions when tested with silver nitrate?

  Very pale yellow precipitate
• What happens to the precipitates when exposed to light?

  They take on grey or purplish tints
• What does the absence of a precipitate with fluoride ions indicate?

  Chloride, bromide, or iodide are absent
• What are the insoluble silver halides formed in the test?

  Silver chloride, silver bromide, silver iodide
• Why does silver fluoride not produce a precipitate?

  It is soluble in water
• What happens to the AgCl precipitate when ammonia solution is added?

  Dissolves to give a colourless solution
• How does AgBr behave when dilute ammonia is added?

  Almost unchanged, dissolves in concentrated ammonia
• What does it mean if the ionic product exceeds the solubility product?

  A precipitate will form
• What does ammonia do to silver ions in the test?

  Forms a stable complex ion
• Why does silver iodide not dissolve in ammonia solution?

  It is too insoluble
• What happens when concentrated sulphuric acid is added to fluoride ions?

  Produces steamy acidic fumes of HF
• What happens when concentrated sulphuric acid is added to chloride ions?

  Produces steamy acidic fumes of HCl