Group 7

• Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values. Suggest, with reasons, the order of melting points for these three substances. (6)


  • SrCl2> ICl > Br>
  • SrCl2 strong ionic bonds / (strong electrostatic attraction between opposite ions)
  • Lattice so many strong bonds to overcome 
  • ICl has dipole-dipole between molecules – weaker than ionic bonds
  • Br2 has van der Waals forces between molecules – much weaker 
• 3 Cl2 + 6 NaOH → NaClO3 + 5 NaCl + 3 H2O Give the oxidation state of chlorine in NaClO3 and in NaCl NaClO3  NaCl   State, in terms of redox, what happens to chlorine in the reaction


  • (+)5 and -1
  • Is oxidised and reduced Allow undergoes disproportionation Allows gains and loses electrons
• State what is observed when aqueous chlorine is added to sodium bromide solution.


  Yellow or orange solution
• State one observation when solid sodium chloride reacts with concentrated sulfuric acid


  Misty fumes 
• State what is observed when silver nitrate solution is added to sodium fluoride solution.


  Colourless solution 
• Silver nitrate is added to the solution.Suggest why an excess is used.


  To ensure all the halide ions are removed from the solution 
• Identify one other sulfur-containing reduction product formed when solid sodium iodide reacts with concentrated sulfuric acid.


  SO2

  H2S
•  A solution that is thought to contain chloride ions and iodide ions is tested.2. Aqueous silver nitrate is added to the solution.3. A pale yellow precipitate forms.4. Excess dilute aqueous ammonia is added to the mixture.5. Some of the precipitate dissolves and a darker yellow precipitateremains.Give a reason for the use of each reagent.Explain the observations.Give ionic equations for any reactions.

  1. Dilute nitric acid is added to the solution.


  answer

  
• Which pair of solutions, when mixed, reacts to form a dark brown solution?

  NaI(aq) + Br2(aq)
• Chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of bleach.Give an equation for this reaction.


  Cl2 + 2 NaOH → NaCl + NaClO + H2O
• Give a reason why chlorine is added to drinking water.


  Kills bacteria / kills microorganisms / kills microbes / kills pathogens
• Give an equation for the reaction of chlorine with water.

  Cl2 + H2O ⇌ HCl + HClO /

  2 Cl2 + 2 H2O → 4 HCl + O2
• Chlorine has a low boiling point because the forces between the moleculesare weak.Explain how these forces arise between molecules of chlorine. (3)


  • Uneven distribution of electrons creates a dipole 
  • Induces a dipole in a neighbouring molecule.
  • (These) temporary dipoles attract / temporary attraction between δ+ and δ
• Test with NH3 for Cl and Br and I


  • Cl- dissolves in dilute NH3
  • Br- dissolves in concentrated NH3
  • I- does not dissolve
• What happens in iodide test


  Yellow precipitate 
• what happens in bromide test 


  Cream precipitate 
• What happens in chlorine test 


  White precipitate 
• Why do you add HNO3 


  To remove unwanted ions (CO3 (2-))
• What is the test for halides 


  Add HNO3 and AgNO3
• Sodium bromide and sulphuric acid equations (2)


  2 equations

  
• Sodium chloride with sulphuric acid equations (2)


  2 equations

  
• What happens to the reducing power down G7


  • Increases because ions get larger 
  • electrons are easily lost 
  • can be oxidised easier so they are better reducing agents 
• Chlorine is toxic but why is it used in water treatment 


  Benefits outweigh risk 
• What is the reaction of chlorine with water in UV/sunlight 


  equation

  
• What is the equation with chlorine and water 


  absence of sunlight 

  
• What is a disproportionation reaction 


  When a species is oxidised and reduced in the same equation 
• Why is formation of bleach a disproportionation reaction 


  Cl is oxidise and reduced 
• What is bleach (formula)

  Sodium chlorate

  NaClO
• What is the equation for the formation of bleach 


  equation

  
• Why is it easier for chlorine to gain an electron 


  • Smaller
  • greater atttaction between nucleus and outer shell electrons 
• What happens to the oxidising power down G7


  decreases
• What is the ionic equation with chlorine and bromine 


  equation

  
• What is the displacement reaction with chlorine and bromine 


  equation

  
• Reactions of G7 with G7 ions 

  Cl2 with KCl/KBr/KI

  Br2 with KCl/KBr/KI

  I2 with KCl/KBr/KI


  equations

  
•  Explain why chlorine has a lower boiling point

   than bromine (2)


  • Chlorine is smaller than bromine
  • Cl2 has weaker / fewer / less (VdW) intermolecular forces / forces between molecules
• 3 unknown samples. These compounds are sodium carbonate, sodium fluoride and sodium chloride.

  Outline a logical sequence of test-tube reactions to identify themInclude the observations.

  Give equations, including state symbols(4)

  • Add sulphuric acid to all three add water. Add AgNO3. Na2CO3 will fizz with acid. NaCl gives white ppt with AgNO3. NaF shows no (visible) change
  • $NaCO_3+$$2HNO_3\ \rightarrow\ CO_2+$$H_2O$
  • $AgNO_3+$$NaCl\ \rightarrow\ AgCl+$$NaNO_3$
• Give a half-equation to show the conversion of iodide ions to iodine.

  Give a half-equation to show the conversion of sulfuric acid to sulfur.Give an overall equation for this redox reaction.



  $2I^{\ -}\rightarrow\ I_2+$$2e^-$

  $H_2SO_4+$$6H^+$$+$$6e^-\ \rightarrow\ S+$$4H_2O+$$6I^-+$$3i_2$
• Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.State one observation made during this reaction.



  $2H_2SO_4+$$2NaBr\ \rightarrow\ SO_2+$$Br_2+$$2H^+$

  • orange/brown fumes/solution
• Sodium iodide with suphuric acid equations (3)


  $NaI+$$H_2SO_4\ \rightarrow\ NaHSO_4+$$HI$

  $2HI+$$H_2SO_4\ \rightarrow\ I_2+$$SO_2+$$2H_2O$

  $6HI+$$SO_2\ \rightarrow\ H_2S+$$3I_2+$$2H_2O$