Group 7

• Why does boiling point increase down the halogen group?

  Stronger van der Waals forces
• What trend occurs in electronegativity down the halogen group?

  Decreases down the group
• What trend occurs in first ionisation energy down the halogen group?

  Decreases down the group
• What is the trend in oxidising ability down the halogen group?

  Decreases down the group
• What happens in a displacement reaction involving halogens?

  A halogen with a stronger oxidising power displaces a halogen with a lower oxidising power
• What is the result of identifying halide ions using acidified silver nitrate?

  Formation of a precipitate
• What is the trend in reducing power of halide ions?

  Increases down the group
• What is the main use of chlorine in water treatment?

  Kills bacteria
• What type of reaction occurs when chlorine reacts with water?

  Disproportionation reaction as chlorine changes its oxidation number from 0 to -1 and 0 to +1
• What is produced when chlorine reacts with cold dilute aqueous NaOH?


  Sodium chlorate (I)
• What is the trend in solubility of silver halides down the group?

  • Solubility decreases down the group
  • Silver fluoride is soluble
  • Silver bromide and iodide are less soluble
• What is the role of dilute nitric acid in halide ion testing?

  • Removes soluble carbonate or hydroxide ions
  • Prevents interference in silver halide precipitation
• Why does electronegativity decrease down the group of halogens?

  Atoms get larger, increasing distance and shielding
• What is bleach made from?

  Chlorine and sodium hydroxide
• What is the risk associated with chlorine reacting with organic compounds?

  Formation of potentially carcinogenic chloroalkanes
• What color precipitate indicates the presence of chloride ions?

  White precipitate
• What color precipitate indicates the presence of bromide ions?

  Cream precipitate
• What color precipitate indicates the presence of iodide ions?

  Yellow precipitate
• What happens to the precipitate of chloride ions when dilute ammonia is added?

  It dissolves
• What happens to the precipitate of bromide ions when concentrated ammonia is added?

  It dissolves
• What happens to the precipitate of iodide ions when concentrated ammonia is added?

  It does not dissolve
• What is the test for ammonium compounds using sodium hydroxide?

  Produces ammonia gas when heated
• What color change occurs when testing for hydroxides with litmus paper?

  Red litmus turns blue
• What gas is produced when hydrochloric acid reacts with carbonates?

  Carbon dioxide gas
• What indicates the presence of sulfate ions when barium chloride is added?

  White precipitate of barium sulfate
• What is the order of tests to identify ions in a sample?

  Carbonates, sulfates, halides
• Why is it important to test for carbonates first?

  To avoid false positives in sulfate tests
• What trend occurs in boiling point down the halogen group?


  Increases down the group
• What is electronegativity?

  The power of an atom to attract a pair of electrons towards itself in a covalent bond
• What is observed when chlorine reacts with potassium bromide? Write the ionic equation

  Cl2(aq) + 2Br−(aq) ➔ 2Cl− (aq) + Br2(aq)

  Chlorine displaces bromide, forming a yellow solution
• What is observed when chlorine reacts with potassium iodide? Write the ionic equation

  Cl2(aq) + 2I−(aq) ➔ 2Cl− (aq) + I2(aq)

  Chlorine displaces iodide, forming a brown solution
• What is observed when bromine reacts with potassium iodide? Write the ionic equation

  Br2(aq) + 2I−(aq) ➔ 2Br− (aq) + I2(aq)

  Bromine displaces Iodide, forming a brown solution
• What is a disproportionation reaction?

  An element is simultaneously oxidised and reduced in the same chemical reaction
• Why is chlorine used in water despite it being toxic?

  The benefits to health of water treatment outweigh its toxic effects
• What is a reducing agent?

  A substance that reduces another atom by causing it to gain electrons as it donates electrons
• What is an oxidising agent?

  A substance that oxidises another atom by causing it to lose electrons as it accepts electrons
• What is observed during the reaction between NaCl and H2SO4? Write the equation and state the type of reaction

  Acid-base reaction

  NaCl(s) + H2SO4(aq) ➔ NaHSO4(aq) + HCl(g)

  White steamy fumes of HCl
• What is observed during the reaction between NaBr and H2SO4? Write the equation and state the type of reaction

  Acid-base reaction

  NaBr(s) + H2SO4(aq) ➔ NaHSO4(aq) + HBr(g)

  White steamy fumes of HBr

  Redox reaction

  2HBr(g) + H2SO4(aq) ➔ Br2(g) + SO2(g) + 2H2O(l)

  Orange fumes of Br2

  Colourless acidic gas SO2
• What is observed during the reaction between NaI and H2SO4? Write the equation and state the type of reaction

  Acid-base reaction

  NaI(s) + H2SO4(aq) ➔ NaHSO4(aq) + HI(g)

  White steamy fumes of HI

  Redox reaction

  2HI(g) + H2SO4(aq) ➔ I2(g) + SO2(g) + 2H2O(l)

  Purple fumes of I2

  Colourless acidic gas SO2

  6HI(g) + H2SO4(g) ➔ S(s) + 3I2(s) + 4H2O(l)

  Yellow solid of S

  8HI(g) + H2SO4(g) ➔ H2S(s) + 4I2(s) + 4H2O(l)

  Rotten egg smell gas H2S
• How does the role of H2SO4 change in an acid-base reaction to a redox reaction?

  Acts as an acid (proton donor) and then acts as an oxidising agent