1. 1
   A fireworks manufacturer is testing several unlabelled metal salt powders to identify which metal ions they contain, using flame tests carried out on a clean wire loop dipped into each powder and held in a roaring blue Bunsen flame.

   (a)

   A fireworks manufacturer wants to check which metal salts are present in different powder samples by carrying out flame tests. When a sample containing sodium ions is held in a Bunsen flame, what colour flame is produced?

   [1 mark]

   • ARed
   • BYellow
   • CLilac
   • DOrange-red

   (b)

   Another sample from the same batch produces a lilac flame colour when tested. Which metal ion is present in this sample?

   [1 mark]

   • ALithium ion (Li+)
   • BCopper ion (Cu2+)
   • CCalcium ion (Ca2+)
   • DPotassium ion (K+)

   (c)

   Describe how the fireworks manufacturer should carry out a flame test on one of the metal salt powder samples.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A plumber and a laboratory chemist are investigating gases released by a leaking industrial pipe joint at a factory, and collect gas samples in test tubes to identify each gas present using standard chemical tests.

   (a)

   A plumber suspects that a leaking pipe joint is releasing a gas. They collect a sample and test it by holding a lit splint at the mouth of the test tube, which produces a squeaky pop. Which gas is present?

   [1 mark]

   • AOxygen
   • BCarbon dioxide
   • CHydrogen
   • DAmmonia

   (b)

   The chemist then tests a second gas sample by bubbling it through limewater, which turns cloudy (milky). Which gas is present in this sample?

   [1 mark]

   • ACarbon dioxide
   • BChlorine
   • CHydrogen
   • DOxygen

   (c)

   Describe the tests, and the results the chemist would observe, to confirm the presence of oxygen gas and ammonia gas in two further samples collected at the factory.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A water-quality laboratory is analysing a sample of well water from a rural community, suspected of containing dissolved ammonium ions, iron ions and various anions such as sulfate, chloride and carbonate ions, and must identify each ion present using standard chemical tests.

   (a)

   A water-quality laboratory receives a sample of well water suspected of containing dissolved ammonium ions and iron(III) ions. Describe how sodium hydroxide solution could be used to test for the presence of ammonium ions and iron(III) ions in the sample, stating the observation that would confirm each ion.

   [3 marks]

   (b)

   Describe how the laboratory could test the same well water sample for the presence of sulfate ions and chloride ions, stating the reagents used and the observation that would confirm each ion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A forensic chemist is investigating an unidentified white crystalline powder recovered from a crime scene, believed to be a mixture of an unknown metal salt, and must use a systematic sequence of chemical tests to determine both the cation and the anion present before reporting findings to the police.

   (a)

   A forensic chemist is investigating a white crystalline powder found at a crime scene, suspected to be a mixture of two unknown salts. Describe, in full detail, a complete sequence of chemical tests the forensic chemist could carry out to identify the cation and the anion present in the mixture, including how a flame test, sodium hydroxide tests and anion tests could each contribute evidence.

   [6 marks]

   (b)

   The forensic chemist's flame test produces an orange-red flame, the sodium hydroxide test shows no gas released and a white precipitate that does not dissolve in excess sodium hydroxide, and the anion tests give a white precipitate with both barium chloride and silver nitrate solutions. Evaluate this evidence to determine which cation and which anion are most likely present, explaining your reasoning and identifying the salt, and discuss any limitations of relying on these tests alone.

   [6 marks]

   Total for question 4: 12 marks

End of questions