1. 1
   A water treatment plant uses chlorine gas to disinfect drinking water, storing it in pressurised cylinders.

   (a)

   What is the appearance of chlorine at room temperature and pressure?

   [1 mark]

   • AA pale yellow-green gas
   • BA red-brown liquid
   • CA grey-black solid
   • DA colourless gas

   (b)

   Chlorine belongs to Group VII of the Periodic Table. What term describes the structure of a chlorine molecule?

   [1 mark]

   • AMonatomic
   • BDiatomic
   • CTriatomic
   • DA giant covalent structure

   (c)

   State the appearance at room temperature and pressure of bromine and iodine, the two halogens below chlorine in Group VII, and describe the general trend in physical state shown by chlorine, bromine and iodine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A school technician adds a small amount of chlorine water (pale yellow-green) to a colourless solution of potassium bromide, and the mixture turns orange.

   (a)

   What has happened in this reaction?

   [1 mark]

   • APotassium has been displaced from the solution
   • BBromine has displaced chlorine from the solution
   • CNo reaction has taken place
   • DChlorine has displaced bromine from potassium bromide

   (b)

   What does this displacement reaction show about the relative reactivity of chlorine and bromine?

   [1 mark]

   • AChlorine is less reactive than bromine
   • BChlorine and bromine are equally reactive
   • CChlorine is more reactive than bromine
   • DReactivity cannot be determined from this reaction

   (c)

   The technician then tests whether bromine water can displace chlorine from a solution of potassium chloride. Predict what would be observed, and explain your prediction using the reactivity trend in Group VII.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A food preservation company wants to understand why chlorine is a more effective disinfectant than iodine, in terms of their relative reactivity as halogens.

   (a)

   Explain, in terms of electronic configuration, why reactivity decreases going down Group VII from chlorine to bromine to iodine.

   [3 marks]

   (b)

   The company also wants to justify this choice using displacement reaction evidence. Describe an experiment, using aqueous solutions of two different halogens and a potassium halide, that would provide evidence to confirm chlorine is more reactive than iodine, and describe the expected observation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry lecturer presents data on the known Group VII halogens: fluorine, chlorine, bromine and iodine show decreasing reactivity in that order, and their appearances at room temperature and pressure are: fluorine, pale yellow gas; chlorine, pale yellow-green gas; bromine, red-brown liquid; iodine, grey-black solid.

   (a)

   Using this data, predict the reactivity and physical state at room temperature and pressure of the next element down the group, astatine, explaining your reasoning.

   [6 marks]

   (b)

   A student in the lecture suggests testing the predicted reactivity of astatine using a displacement reaction with iodine, similar to the tests used earlier for chlorine, bromine and iodine. Explain what result would be expected if astatine solution were added to a solution containing iodide ions, and what result would be expected if iodine solution were added to a solution containing astatide ions, based on the predicted trend.

   [6 marks]

   Total for question 4: 12 marks

End of questions