Group 7 trends and halogen reactionsEdexcel International A Level Chemistry: Subtopic test

1. 1
   The melting and boiling temperatures of three halogens are: chlorine, Cl₂, melting 172 K and boiling 239 K; bromine, Br₂, melting 266 K and boiling 332 K; iodine, I₂, melting 387 K and boiling 457 K. Room temperature is taken as 298 K.

   (a)

   What is the physical state of bromine at room temperature?

   [1 mark]

   • ALiquid
   • BSolid
   • CGas
   • DAqueous solution

   (b)

   Which type of force must be overcome when iodine melts?

   [1 mark]

   • ACovalent bonds within the I₂ molecules
   • BIonic bonds between iodide ions
   • CLondon forces between I₂ molecules
   • DHydrogen bonds between I₂ molecules

   (c)

   Explain why the boiling temperature increases from chlorine to iodine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds a few drops of aqueous halogen solutions to separate aqueous solutions of potassium halides. She then adds a few cm³ of hexane to each tube, shakes it and leaves the layers to separate.

   (a)

   Aqueous chlorine is added to aqueous potassium bromide, followed by hexane. What is the colour of the upper hexane layer?

   [1 mark]

   • AColourless
   • BOrange
   • CPurple
   • DPale green

   (b)

   Which mixture shows no displacement reaction?

   [1 mark]

   • AAqueous chlorine and aqueous potassium iodide
   • BAqueous chlorine and aqueous potassium bromide
   • CAqueous bromine and aqueous potassium iodide
   • DAqueous iodine and aqueous potassium bromide

   (c)

   Write the ionic equation for the reaction of aqueous bromine with aqueous iodide ions, and identify the oxidising agent.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A swimming pool is treated with chlorine to kill bacteria. A manufacturer makes bleach by passing chlorine into cold dilute aqueous sodium hydroxide, forming sodium chloride and sodium chlorate(I), NaClO. When the sodium hydroxide is hot and concentrated, sodium chlorate(V), NaClO₃, forms instead of NaClO.

   (a)

   Write the equation for the reaction of chlorine with water. Use oxidation numbers to show that this is disproportionation, and state why it is useful in treating water.

   [3 marks]

   (b)

   Write the equation for the reaction of chlorine with hot concentrated sodium hydroxide. Give the oxidation numbers of chlorine in the two products and explain why the reaction is disproportionation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Chlorine, bromine and iodine are all in Group 7. A teacher prepares aqueous solutions of the three halogens and of potassium chloride, potassium bromide and potassium iodide, together with hexane, for a class demonstration of the properties and reactivity of the halogens.

   (a)

   Explain, using displacement reactions and equations, why chlorine is a stronger oxidising agent than bromine, and bromine than iodine, and explain the trend in terms of atomic structure.

   [6 marks]

   (b)

   Describe the appearance of chlorine, bromine and iodine as elements at room temperature and when dissolved in hexane. Write equations for the reactions of chlorine with sodium and of bromine with magnesium, and explain these in terms of oxidation numbers.

   [6 marks]

   Total for question 4: 12 marks

End of questions