1. 1
   An environmental monitoring station analyses a sample of dry air and records the approximate percentage, by volume, of each gas present, then compares this with a sample taken near a busy industrial site.

   (a)

   Which gas makes up the largest proportion, by volume, of dry air?

   [1 mark]

   • ANitrogen, at approximately 78%
   • BOxygen, at approximately 78%
   • CCarbon dioxide, at approximately 21%
   • DArgon, at approximately 21%

   (b)

   Which of the following correctly lists the approximate percentages, by volume, of the four most abundant gases in dry air?

   [1 mark]

   • ANitrogen 78%, carbon dioxide 21%, oxygen just under 1%, argon about 0.04%
   • BNitrogen 21%, oxygen 78%, argon just under 1%, carbon dioxide about 0.04%
   • COxygen 78%, carbon dioxide 21%, nitrogen just under 1%, argon about 0.04%
   • DNitrogen 78%, oxygen 21%, argon just under 1%, carbon dioxide about 0.04%

   (c)

   The monitoring station finds that the sample taken near the industrial site has a slightly higher percentage of carbon dioxide than the sample taken in the countryside. Suggest a reason for this difference and explain why an increase in atmospheric carbon dioxide is a cause for environmental concern.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A fireworks factory technician burns a strip of magnesium ribbon in air to test its brightness for a display, producing an intense white flame and leaving behind a white solid residue, which is collected and weighed.

   (a)

   A fireworks factory burns a strip of magnesium ribbon in air to test its brightness, producing an intense white flame and a white solid residue. Which gas in the air is magnesium reacting with to form this white solid?

   [1 mark]

   • ACarbon dioxide
   • BNitrogen
   • COxygen
   • DArgon

   (b)

   The technician also burns a small sample of sulfur in air as part of the same test. Which statement correctly describes the product of this combustion?

   [1 mark]

   • ASulfur reacts with nitrogen in the air to form a white solid residue, as magnesium does
   • BSulfur reacts with oxygen in the air to form sulfur dioxide gas
   • CSulfur does not react with any gas in the air when burned
   • DSulfur reacts with argon in the air to form an unreactive compound

   (c)

   Write balanced symbol equations, including state symbols, for the combustion of magnesium in oxygen and for the combustion of sulfur in oxygen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student places a small piece of damp iron wool at the closed end of a test tube, seals the tube so the trapped air cannot escape or be replaced, and stands it upside down over a trough of water for several days, measuring how far the water rises inside the tube.

   (a)

   Describe how this experiment can be used to determine the approximate percentage of oxygen in air.

   [3 marks]

   (b)

   The student's results show that the water rises to fill approximately one fifth of the original volume of trapped air. Use this result to calculate the approximate percentage of oxygen in the air sample, and explain one reason why this method might give a slightly inaccurate result if not carried out carefully.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A geology student heats a sample of green copper(II) carbonate strongly in a test tube in a school laboratory and observes that the solid turns black, while a gas is given off that turns limewater cloudy when bubbled through it.

   (a)

   A geology student heats a sample of copper(II) carbonate strongly in a test tube and observes that the green solid turns black, while a gas is given off that turns limewater cloudy. Describe what is happening in this experiment, including a word equation and a balanced symbol equation, and explain why this type of reaction is classified as thermal decomposition.

   [6 marks]

   (b)

   The student notes that the carbon dioxide produced in this experiment is the same gas that has been steadily increasing in concentration in the Earth's atmosphere due to human activity. Explain why carbon dioxide is described as a greenhouse gas, and explain the link between rising atmospheric carbon dioxide levels and climate change.

   [6 marks]

   Total for question 4: 12 marks

End of questions