Uses of chlorine and chlorate(I)AQA A-Level Chemistry: Subtopic test

1. 1
   Chlorine gas is bubbled into water in a laboratory. The pale green solution formed is acidic and has bleaching properties.

   (a)

   What are the oxidation states of chlorine in Cl₂, Cl⁻ and ClO⁻ respectively?

   [1 mark]

   • A0, −1, −1
   • B0, −1, +1
   • C0, +1, −1
   • D−1, 0, +1

   (b)

   Which term describes a reaction in which the same element is both oxidised and reduced?

   [1 mark]

   • ANeutralisation
   • BDisplacement
   • CDisproportionation
   • DHydrolysis

   (c)

   Write an equation for the reaction of chlorine with water that forms chloride ions and chlorate(I) ions, and explain why the reaction is a disproportionation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A local council treats its drinking water by adding chlorine. A resident complains that chlorine is a poisonous gas and asks why it is added to the water supply.

   (a)

   What is the main reason chlorine is added to drinking water?

   [1 mark]

   • ATo remove dissolved carbon dioxide
   • BTo raise the pH of the water
   • CTo precipitate metal ions
   • DTo kill bacteria and other microorganisms

   (b)

   Which species formed when chlorine reacts with water is mainly responsible for killing microorganisms?

   [1 mark]

   • AClO⁻ ions
   • BCl⁻ ions
   • CH⁺ ions
   • DO₂ molecules

   (c)

   Explain why the benefit to health of treating drinking water with chlorine is considered to outweigh its toxic effects.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A swimming pool manager makes a bleach solution by reacting chlorine gas with cold, dilute aqueous sodium hydroxide. She also considers adding chlorine gas directly to the pool water.

   (a)

   Write an equation for the reaction of chlorine with cold, dilute aqueous sodium hydroxide, name the chlorine-containing compound in the solution that acts as the bleach, and state one other use of the solution.

   [3 marks]

   (b)

   Use oxidation states to show that the reaction of chlorine with cold, dilute aqueous sodium hydroxide is a disproportionation reaction.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A town's water company adds chlorine to the supply. A campaign group argues that, because chlorine is toxic and can form harmful compounds with organic matter in water, it should no longer be added. The company stores the water in open reservoirs exposed to strong sunlight before it is distributed.

   (a)

   Evaluate the campaign group's argument. Include an equation for the reaction of chlorine with water and discuss the advantages and disadvantages of adding chlorine to water supplies.

   [6 marks]

   (b)

   Explain, using equations and oxidation states, why the chlorine concentration in the water falls when it is stored in sunlight, and why the company should add the chlorine after storage rather than before.

   [6 marks]

   Total for question 4: 12 marks

End of questions