1. 1
   A student gently heats a mixture of ammonium chloride and calcium hydroxide in a test tube, releasing a colourless gas with a sharp, choking smell. The student holds a piece of damp red litmus paper at the mouth of the test tube.

   (a)

   Which observation confirms the gas is ammonia?

   [1 mark]

   • AThe damp red litmus paper turns blue
   • BThe damp red litmus paper stays red
   • CThe damp red litmus paper bleaches white
   • DA squeaky pop is heard

   (b)

   Why must the litmus paper be damp rather than dry for this test to work effectively?

   [1 mark]

   • AThe gas needs to dissolve in the moisture on the paper to form an alkaline solution
   • BDry paper reacts explosively with ammonia
   • CDamp paper is a different colour to dry paper before testing
   • DThe gas cannot be detected on dry paper because it is denser than air

   (c)

   Describe how the student could carry out a second, independent test on the gas using hydrogen chloride gas, and state the result that would be observed if the gas is confirmed to be ammonia.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A farmer stores a bottle of concentrated ammonia solution used for making fertiliser. A worker opens the bottle and notices a strong, sharp, choking smell.

   (a)

   Which property of the gas released is being described here?

   [1 mark]

   • AIts characteristic odour
   • BIts density
   • CIts melting point
   • DIts colour

   (b)

   To confirm the gas escaping from the bottle is ammonia rather than another sharp-smelling gas, the worker holds damp red litmus paper near the opening. What colour change would confirm ammonia is present?

   [1 mark]

   • ABlue to red
   • BRed to blue
   • CRed bleaches to white
   • DNo colour change occurs

   (c)

   Explain, in terms of the type of solution formed, why ammonia gas turns damp red litmus paper blue rather than red.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A quality control chemist at a cleaning products factory needs to confirm whether a returned batch of window cleaner still contains ammonia, as stated on the label, before it can be resold.

   (a)

   Describe a full procedure the chemist could use, involving two independent tests, to confirm the presence of ammonia gas released from a warmed sample of the cleaner.

   [3 marks]

   (b)

   The chemist finds that the damp red litmus paper turns blue, but no white smoke forms when the acid-dipped glass rod is brought near the tube. Explain this apparently contradictory result, and suggest what the chemist should do next before reaching a conclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An agricultural inspector visits a fertiliser plant and must confirm whether gas escaping from a leaking storage tank is ammonia, since this would require an immediate safety response.

   (a)

   Describe, in detail, how the inspector could safely confirm the identity of the gas using appropriate tests, and explain the reasoning behind each observation.

   [6 marks]

   (b)

   The inspector obtains a positive litmus result (red turns blue) but the white smoke test gives an unclear result on the first attempt. Evaluate the reliability of relying on the litmus test alone in this safety-critical situation, and discuss what additional evidence or precautions the inspector should use before declaring the leak confirmed as ammonia.

   [6 marks]

   Total for question 4: 12 marks

End of questions