1. 1
   A firework manufacturer wants to check that a batch of metal salt powder intended for a red-orange firework display actually contains calcium ions, rather than a different metal salt that was accidentally mixed in during production.

   (a)

   A small sample is held in a hot flame using a clean nichrome wire. Which flame colour would confirm the presence of calcium ions?

   [1 mark]

   • AOrange-red
   • BCrimson
   • CLilac
   • DGreen

   (b)

   The manufacturer also tests a second powder that should give a lilac flame for a purple firework effect. Which metal ion is responsible for a lilac flame colour?

   [1 mark]

   • ASodium
   • BPotassium
   • CCopper
   • DLithium

   (c)

   The manufacturer is concerned that one powder sample might actually be a mixture of two different metal salts rather than a single pure salt. Explain why a flame test alone might not reliably identify all the metal ions present in a mixed sample.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hospital laboratory receives a water sample from a patient's home suspected of containing dissolved copper compounds from old plumbing pipes.

   (a)

   A technician adds sodium hydroxide solution dropwise to the sample. Which observation would confirm the presence of copper(II) ions?

   [1 mark]

   • AA white precipitate forms that dissolves in excess sodium hydroxide
   • BA green precipitate forms
   • CA blue precipitate forms
   • DA brown precipitate forms

   (b)

   The same laboratory also tests a second water sample suspected of containing aluminium ions leached from corroded aluminium fittings. Sodium hydroxide is added, first dropwise and then in excess. Which result would confirm aluminium ions specifically, rather than calcium or magnesium ions?

   [1 mark]

   • AA white precipitate forms and does not dissolve in excess sodium hydroxide
   • BNo precipitate forms at any point
   • CA blue precipitate forms and does not dissolve in excess
   • DA white precipitate forms and dissolves when excess sodium hydroxide is added

   (c)

   The laboratory technician also needs to write a word or balanced symbol equation to record the reaction confirming iron(II) ions in a third sample using sodium hydroxide solution. Write the balanced symbol equation, including state symbols, for the reaction between iron(II) ions and hydroxide ions to form the precipitate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An environmental agency is investigating whether a river downstream of a tannery is contaminated with dissolved sulfate ions from leather-processing waste.

   (a)

   Describe how the agency's chemist could test a water sample for the presence of sulfate ions, including the reagents needed and the expected positive result.

   [3 marks]

   (b)

   The agency also suspects the river water contains dissolved halide ions from a nearby chemical plant, and wants to determine specifically whether chloride, bromide or iodide ions are present. Describe the full test procedure and explain how the chemist would distinguish between the three different halide ions based on the results.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A quality control chemist at a fertiliser company receives an unlabelled sample of a soluble metal salt and must identify both the metal ion and any anion present using only flame tests, sodium hydroxide solution, and precipitation tests for anions, without access to any instrumental analysis equipment.

   (a)

   Describe a complete, logical testing sequence the chemist could follow to identify an unknown metal ion (choosing from lithium, sodium, potassium, calcium, copper, aluminium, iron(II) or iron(III)) and an unknown anion (choosing from carbonate, chloride, bromide, iodide or sulfate), explaining what result at each stage would allow the chemist to draw a conclusion.

   [6 marks]

   (b)

   After testing, the chemist obtains a clear lilac flame colour when a control sample known to be potassium sulfate is tested. However, for the unknown fertiliser sample, the flame test gives an ambiguous pale colour that is hard to distinguish, and the technician wonders whether a mixture of potassium and sodium ions might be present. Explain why this ambiguity occurs, and describe how flame emission spectroscopy could resolve the uncertainty that the simple flame test cannot, referring to the advantages of instrumental methods over chemical tests.

   [6 marks]

   Total for question 4: 12 marks

End of questions