1. 1
   A technician reacts a small piece of magnesium ribbon with dilute hydrochloric acid in a test tube, producing a colourless gas. To test whether the gas is hydrogen, the technician holds a lighted splint at the mouth of the test tube.

   (a)

   Which observation would confirm the gas is hydrogen?

   [1 mark]

   • AThe splint relights
   • BA squeaky pop is heard
   • CThe splint is extinguished immediately
   • DThe gas turns limewater cloudy

   (b)

   The technician collects the gas by displacement of water in an inverted test tube. Why is this collection method suitable for hydrogen gas?

   [1 mark]

   • AHydrogen reacts with water
   • BHydrogen is denser than air
   • CHydrogen is insoluble in water
   • DHydrogen turns limewater cloudy

   (c)

   Describe exactly how the technician should carry out the lighted splint test on the gas collected, and describe the result that would be observed if the gas is hydrogen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   During the electrolysis of dilute sulfuric acid, a colourless gas collects at the negative electrode (cathode). A student wants to confirm that this gas is hydrogen.

   (a)

   Which piece of equipment should the student use to carry out the confirming test?

   [1 mark]

   • AA glowing splint
   • BDamp red litmus paper
   • CLimewater in a test tube
   • DA lighted splint

   (b)

   The student carries out the test and hears a squeaky pop. What does this result confirm about the gas collected at the cathode?

   [1 mark]

   • AThe gas is hydrogen
   • BThe gas is carbon dioxide
   • CThe gas is oxygen
   • DThe gas is chlorine

   (c)

   Explain why it is important for the student to collect a reasonably pure sample of the gas in the test tube (rather than a mixture heavily diluted with air) before applying the lighted splint test, referring to what a false or unclear result might look like.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A laboratory technician needs to demonstrate the test for hydrogen gas safely to a class, using zinc granules and dilute hydrochloric acid to generate the gas in a boiling tube.

   (a)

   Describe the full method the technician should follow, from generating the gas to confirming its identity, including one safety precaution.

   [3 marks]

   (b)

   One student in the class suggests using a glowing splint instead of a lighted splint to save time. Explain why this would not correctly identify the gas, and describe what result would actually be observed with a glowing splint if the gas were hydrogen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A researcher is investigating whether a gas sample collected from a fuel cell is hydrogen, oxygen, or a mixture of the two, before it is used in a demonstration.

   (a)

   Describe, in detail, a full experimental procedure the researcher could use, including exact tests and expected observations, to distinguish between these three possibilities.

   [6 marks]

   (b)

   The researcher obtains an ambiguous result: a faint pop is heard with the lighted splint, but the splint is extinguished rather than relit. Evaluate possible explanations for this ambiguous result and suggest how the researcher could improve the experiment to obtain a clearer conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions