Reactions of halide ionsAQA A-Level Chemistry: Subtopic test

1. 1
   A technician reacts solid sodium chloride, solid sodium bromide and solid sodium iodide, in separate tests in a fume cupboard, with concentrated sulfuric acid.

   (a)

   Which observation is made when solid sodium chloride reacts with concentrated sulfuric acid?

   [1 mark]

   • AOrange-brown fumes
   • BA yellow solid and a smell of bad eggs
   • CPurple vapour
   • DSteamy white fumes

   (b)

   Which change in the oxidation state of sulfur occurs when hydrogen bromide reduces concentrated sulfuric acid to sulfur dioxide?

   [1 mark]

   • A+6 to +4
   • B+6 to 0
   • C+4 to +6
   • D+6 to −2

   (c)

   Chloride ions do not reduce concentrated sulfuric acid but iodide ions do. Explain why iodide ions are the better reducing agent.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student has a colourless aqueous solution of an unknown sodium halide. She adds dilute nitric acid followed by aqueous silver nitrate and obtains a cream precipitate.

   (a)

   Which pair correctly identifies the halide ion in the solution and the precipitate formed?

   [1 mark]

   • ACl⁻ and AgCl
   • BI⁻ and AgI
   • CBr⁻ and AgBr
   • DBr⁻ and Ag₂Br

   (b)

   Which reagent should be used to acidify the solution before the silver nitrate is added?

   [1 mark]

   • ADilute hydrochloric acid
   • BDilute nitric acid
   • CDilute sulfuric acid
   • DEthanoic acid

   (c)

   The student adds dilute ammonia solution to the cream precipitate and then concentrated ammonia solution. State what she observes and how this confirms the halide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is given a colourless aqueous solution that may contain carbonate ions, sulfate ions and chloride ions. She tests separate portions of the solution.

   (a)

   Describe the tests she should carry out to show that the solution contains carbonate ions and sulfate ions, and the positive result for each.

   [3 marks]

   (b)

   The solution is found to contain carbonate ions and chloride ions only. Explain why dilute nitric acid must be added before silver nitrate when testing for chloride ions, and write ionic equations for the reaction of the acid with carbonate ions and for the positive test for chloride ions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Three colourless aqueous solutions, labelled X, Y and Z, are known to be sodium chloride, sodium bromide and sodium iodide in some order. One student plans to identify them using acidified silver nitrate followed by ammonia solution. A second student plans to use the solid sodium halides with concentrated sulfuric acid.

   (a)

   Describe how acidified silver nitrate followed by ammonia solution can be used to distinguish X, Y and Z. Include the observations expected, an ionic equation for the precipitation and the reason ammonia solution is needed.

   [6 marks]

   (b)

   Explain the differences in the products and observations when solid sodium chloride, sodium bromide and sodium iodide each react with concentrated sulfuric acid, in terms of the trend in reducing ability of the halide ions.

   [6 marks]

   Total for question 4: 12 marks

End of questions