Group 7: the halogensIB MYP Chemistry: Subtopic test

1. 1
   A nurse in a clinic in Nairobi cleans a patient's cut with a brown iodine solution before applying a dressing. Iodine is a Group 7 element, one of the halogens.

   (a)

   What is the appearance of iodine at room temperature?

   [1 mark]

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

   (b)

   Which formula represents a molecule of iodine?

   [1 mark]

   • AI
   • BI⁻
   • CI₂
   • DI₄

   (c)

   Explain why the nurse uses iodine solution on the cut.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chemist adds a few drops of orange bromine water to a colourless solution of potassium iodide, and the mixture turns brown. She then adds bromine water to a colourless solution of potassium chloride and sees no change.

   (a)

   Which is the best explanation of the brown colour?

   [1 mark]

   • ABromine is less reactive than iodine, so potassium has been displaced
   • BBromine is more reactive than iodine, so iodine has been displaced from the solution
   • CChlorine has formed from the potassium iodide
   • DThe potassium iodide has been neutralised

   (b)

   Which mixture would produce a displacement reaction?

   [1 mark]

   • AIodine solution and potassium bromide solution
   • BBromine water and potassium chloride solution
   • CIodine solution and potassium chloride solution
   • DChlorine water and potassium iodide solution

   (c)

   Write the balanced symbol equation for the reaction of bromine with potassium iodide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A data book gives these melting and boiling points. Chlorine melts at −101 °C and boils at −34 °C. Bromine melts at −7 °C and boils at 59 °C. Iodine melts at 114 °C and boils at 184 °C. A chemist wants to predict the properties of fluorine, which lies above chlorine in Group 7. Room temperature is 25 °C.

   (a)

   State the physical state of chlorine, bromine and iodine at 25 °C.

   [3 marks]

   (b)

   Describe the trend in melting and boiling points down the group and use it to predict the physical state of fluorine at 25 °C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A water treatment works in Nairobi uses chlorine to make drinking water safe. Its laboratory trains new staff using halogen displacement reactions: chlorine water is added to potassium bromide solution and to potassium iodide solution, and iodine solution is added to potassium bromide solution. A councillor has asked whether the works should keep using chlorine, because chlorine gas is toxic and the water can taste of it.

   (a)

   Explain, using electronic structure, why chlorine displaces bromine from potassium bromide solution but iodine does not.

   [6 marks]

   (b)

   Discuss and evaluate whether the works should keep using chlorine to treat drinking water.

   [6 marks]

   Total for question 4: 12 marks

End of questions