Reactions of halides and silver nitrateEdexcel A-Level Chemistry: Subtopic test

1. 1
   A technician adds concentrated sulfuric acid, in a fume cupboard, to separate samples of solid sodium chloride, sodium bromide and sodium iodide.

   (a)

   Which observations are made when concentrated sulfuric acid is added to solid sodium iodide?

   [1 mark]

   • ASteamy fumes only, with no other change
   • BOrange-brown fumes and a colourless choking gas
   • CPurple fumes, a yellow solid and a gas smelling of rotten eggs
   • DA white precipitate and a colourless odourless gas

   (b)

   Hydrogen iodide reduces concentrated sulfuric acid but hydrogen chloride does not. Which statement best explains this?

   [1 mark]

   • AThe iodide ion is larger, so its outer electron is further from the nucleus and more shielded, and is lost more easily
   • BThe H–I bond is stronger than the H–Cl bond, so HI releases electrons more easily
   • CIodine is more electronegative than chlorine, so iodide ions hold electrons more tightly
   • DThe iodide ion is smaller than the chloride ion, so electrons are lost more readily

   (c)

   Hydrogen iodide reduces sulfuric acid to hydrogen sulfide, H₂S. Deduce the change in oxidation number of sulfur and write a balanced equation for the reaction, in which iodine is also formed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician has three unlabelled aqueous solutions, each containing one of sodium chloride, sodium bromide and sodium iodide. She has dilute nitric acid, aqueous silver nitrate, dilute aqueous ammonia and concentrated aqueous ammonia.

   (a)

   A yellow precipitate forms when silver nitrate is added to one solution, and it does not dissolve in concentrated aqueous ammonia. Which halide ion is present?

   [1 mark]

   • AChloride, because silver chloride is yellow
   • BBromide, because silver bromide is yellow and insoluble in ammonia
   • CFluoride, because silver fluoride is a yellow precipitate
   • DIodide, because silver iodide is insoluble even in concentrated ammonia

   (b)

   Which ionic equation, with state symbols, represents the formation of the white precipitate with chloride ions?

   [1 mark]

   • AAg⁺(aq) + Cl⁻(aq) → AgCl(aq)
   • BAg⁺(aq) + Cl⁻(aq) → AgCl(s)
   • CAg⁺(aq) + 2Cl⁻(aq) → AgCl₂(s)
   • DAg(s) + Cl⁻(aq) → AgCl(s)

   (c)

   The precipitate formed in one solution is white and dissolves completely in dilute aqueous ammonia. Identify the halide ion present and give the formula of the ion that makes the precipitate dissolve.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician adds concentrated sulfuric acid to solid sodium chloride in a fume cupboard. She tests the steamy fumes with a glass rod dipped in concentrated ammonia solution and by bubbling them into water. She then repeats the experiment with solid sodium bromide, which also gives orange-brown fumes and a colourless gas with a choking smell.

   (a)

   Explain the three observations made with sodium chloride, using equations where appropriate.

   [3 marks]

   (b)

   Explain the extra observations with sodium bromide by writing the half-equation for the oxidation and the half-equation for the reduction, then the overall equation. State why sodium chloride does not give these extra products.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician must find out which of three unlabelled white solids is sodium chloride, sodium bromide or sodium iodide. She has dilute nitric acid, aqueous silver nitrate, dilute and concentrated aqueous ammonia, and concentrated sulfuric acid, and she works in a fume cupboard.

   (a)

   Describe a sequence of tests using silver nitrate and ammonia that would allow her to identify each halide in aqueous solution. Give the observations and an ionic equation.

   [6 marks]

   (b)

   Compare what is seen when concentrated sulfuric acid is added to solid sodium chloride and to solid sodium iodide, and explain the difference using oxidation numbers and the trend in reducing ability of the halide ions.

   [6 marks]

   Total for question 4: 12 marks

End of questions