Composition of the atmosphereIB MYP Chemistry: Subtopic test

1. 1
   A diving equipment supplier in Cape Town fills cylinders with compressed dry air. Dry air is a mixture of gases. It is mainly nitrogen and oxygen, with small amounts of argon and carbon dioxide.

   (a)

   Approximately what percentage of dry air is nitrogen?

   [1 mark]

   • A21%
   • B0.04%
   • C78%
   • D99%

   (b)

   Which gas is present in the smallest percentage in dry air?

   [1 mark]

   • ANitrogen
   • BOxygen
   • CArgon
   • DCarbon dioxide

   (c)

   The gases other than nitrogen and oxygen make up about 1% of dry air. Name the gas that is the largest part of this 1%, and state the name of the group of elements to which it belongs.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Mumbai measures the percentage of oxygen in air. She puts 100 cm³ of air in a gas syringe that is connected through a tube of heated copper turnings to a second, empty syringe. She pushes the air slowly back and forth over the hot copper until the volume stops changing. When the apparatus has cooled to room temperature, the volume of gas left is 79 cm³.

   (a)

   What colour change shows that the copper is reacting with oxygen?

   [1 mark]

   • AOrange-brown to black
   • BBlack to brown
   • CBrown to blue
   • DIt stays the same colour

   (b)

   Why does the student let the apparatus cool before reading the final volume?

   [1 mark]

   • AHot gases take up less volume than cold gases
   • BHot gases take up more volume than cold gases, so a hot reading would be too large
   • CThe copper only reacts with oxygen when it is cold
   • DOxygen is released from the copper as it cools

   (c)

   Use the results to calculate the percentage of oxygen in the air sample.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Scientists believe that 4 billion years ago the atmosphere of the Earth contained mostly carbon dioxide, with water vapour and nitrogen released by volcanoes, and almost no oxygen. Today, carbon dioxide makes up about 0.04% of the air and oxygen makes up about 21%.

   (a)

   Describe how the percentage of carbon dioxide in the atmosphere decreased as the Earth cooled.

   [3 marks]

   (b)

   Explain how the amount of oxygen in the atmosphere increased over millions of years.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Scientists have measured the percentage by volume of carbon dioxide in the atmosphere: 0.028% in 1800, 0.030% in 1900, 0.032% in 1960, 0.037% in 2000 and 0.041% in 2020. A government in South-East Asia is considering a national tree-planting programme on one million hectares of former farmland to absorb carbon dioxide. The trees would take about 20 years to grow fully, and the land currently grows rice for local farmers.

   (a)

   Discuss the benefits and drawbacks of the tree-planting programme, and reach a justified conclusion.

   [6 marks]

   (b)

   Process the data. Describe the trend, calculate the percentage increase in carbon dioxide between 1800 and 2020, and give two human activities that help to explain the trend.

   [6 marks]

   Total for question 4: 12 marks

End of questions