Group 7: the halogensEdexcel A-Level Chemistry: Subtopic test

1. 1
   A technician compares the Group 7 elements chlorine, bromine and iodine in a fume cupboard at room temperature (about 20 °C).

   (a)

   Which row correctly gives the physical states of chlorine, bromine and iodine at room temperature?

   [1 mark]

   • AChlorine gas, bromine gas, iodine solid
   • BChlorine gas, bromine liquid, iodine solid
   • CChlorine liquid, bromine liquid, iodine solid
   • DChlorine gas, bromine solid, iodine solid

   (b)

   Which statement explains why electronegativity decreases from chlorine to iodine?

   [1 mark]

   • AThe nuclear charge decreases down the group, so the attraction for the bonding pair falls
   • BThe number of outer-shell electrons increases down the group
   • CThe molecules become heavier, so London forces between them are stronger
   • DThe atomic radius and shielding increase, so the nucleus attracts the bonding pair less strongly

   (c)

   Explain why iodine has a higher boiling temperature than chlorine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates displacement reactions of the halogens. She has aqueous solutions of potassium chloride, potassium bromide and potassium iodide, together with chlorine water, bromine water, aqueous iodine and the organic solvent cyclohexane, which is less dense than water and immiscible with it.

   (a)

   Chlorine water is added to potassium iodide solution, cyclohexane is added, and the mixture is shaken and left to settle. What is seen in the upper (cyclohexane) layer?

   [1 mark]

   • AA violet solution
   • BAn orange solution
   • CA pale green solution
   • DA colourless solution

   (b)

   Chlorine water is added to potassium bromide solution: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂. Which species is oxidised, and why?

   [1 mark]

   • AChlorine, because its oxidation number decreases from 0 to −1
   • BChloride ions, because they are formed in the reaction
   • CBromide ions, because their oxidation number increases from −1 to 0
   • DBromine, because it is formed as a product

   (c)

   The student adds aqueous iodine to potassium bromide solution and sees no reaction. Explain this, referring to the relative oxidising power of bromine and iodine.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A water company treats drinking water with chlorine to kill bacteria. A separate factory makes household bleach by passing chlorine into sodium hydroxide solution.

   (a)

   Chlorine reacts with water as it dissolves. Write an equation for the reaction and explain, in terms of oxidation numbers, why it is a disproportionation reaction.

   [3 marks]

   (b)

   Bleach forms when chlorine reacts with cold, dilute sodium hydroxide solution. Write the equation for this reaction and state the oxidation numbers of chlorine in the two chlorine-containing products. Then write the equation for the reaction of chlorine with hot sodium hydroxide solution, giving the oxidation number of chlorine in the extra product.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The boiling temperatures of the first four halogens are: fluorine −188 °C, chlorine −34 °C, bromine 59 °C and iodine 184 °C. Astatine is radioactive with a very short half-life, so it has never been studied in bulk and its properties must be predicted from the trends in the group.

   (a)

   Explain the trend in boiling temperature from fluorine to iodine, and the trend in oxidising power of the halogens down the group.

   [6 marks]

   (b)

   Predict the physical state and colour of astatine at room temperature, and whether astatine would displace iodide ions from solution. Predict how fluorine and astatide ions would behave as oxidising and reducing agents respectively, and evaluate how reliable your predictions are.

   [6 marks]

   Total for question 4: 12 marks

End of questions