1. 1
   A student dips a clean nichrome wire loop into an unknown white powder, holds it in a blue Bunsen flame, and observes a crimson (deep red) colour.

   (a)

   Which metal ion is most likely present in the powder?

   [1 mark]

   • ASodium
   • BLithium
   • CPotassium
   • DBarium

   (b)

   The student then tests a second unknown powder and observes a lilac flame colour. Which metal ion is most likely present in this second powder?

   [1 mark]

   • APotassium
   • BCalcium
   • CSodium
   • DBarium

   (c)

   Describe how the student should clean the nichrome wire loop before testing the second powder, and explain why this step is essential for obtaining a reliable result.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A firework manufacturer wants a particular firework to burn with a brick-red flame.

   (a)

   Which metal compound should be added to the firework mixture to achieve this colour?

   [1 mark]

   • AA lithium compound
   • BA barium compound
   • CA sodium compound
   • DA calcium compound

   (b)

   The manufacturer wants a different firework to burn with a bright green flame instead. Which metal compound should be used?

   [1 mark]

   • AA sodium compound
   • BA potassium compound
   • CA barium compound
   • DA lithium compound

   (c)

   The manufacturer also wants to avoid accidentally including any sodium compounds in either firework, as sodium's flame colour is very strong. Explain why even a small amount of sodium contamination could be a problem for producing a clear calcium red or barium green flame colour.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A school technician needs to carry out the required practical to identify the metal ion in an unknown compound using flame testing techniques, ready for a class demonstration.

   (a)

   Describe the full step-by-step method the technician should follow, from preparing the equipment to recording a result.

   [3 marks]

   (b)

   During the demonstration, the flame colour appears to be a pale, washed-out yellow, and the technician is not fully confident it is sodium rather than a weak, contaminated result. Explain what factors could cause this uncertain result, and describe what the technician should do to reach a confident, reliable conclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A forensic laboratory receives five unlabelled compounds recovered from a crime scene and needs to identify which metal ion (from lithium, sodium, potassium, calcium and barium) each compound contains using flame tests, so that the results can be used as evidence.

   (a)

   Describe, in detail, the full procedure the laboratory should follow to carry out reliable flame tests on all five samples, including the reference colours expected for each metal ion.

   [6 marks]

   (b)

   One of the five samples produces a red flame colour, but the laboratory analyst is unsure whether it is genuinely calcium or a weaker crimson from lithium contaminated with something else. Evaluate the challenges of distinguishing between similar flame colours by eye, and discuss what additional steps the laboratory should take to reach a scientifically defensible conclusion suitable for use as evidence.

   [6 marks]

   Total for question 4: 12 marks

End of questions