Chemistry - Carbon Dioxide (AQA Syllabus A)

Changes which take place and have taken place in the Earth's crust, biosphere and atmosphere are all studied in GCSE Science. This is the last of three quizzes on that topic and it looks in particular at carbon dioxide and the carbon cycle.

The Earth's atmosphere has undergone many dramatic changes since it was formed around four billion years ago - and it is still changing today. It has been much the same for the last 200 million years or so and provides the conditions needed for life as we know it on Earth. Recently, human activities have resulted in further changes in Earth's atmosphere. One of the gases that we send into the atmosphere is carbon dioxide. This is thought by many to be causing changes to the world's climate.

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Most of the carbon dioxide we put into the atmosphere comes from burning fuels, making cement and countless other processes that we use to make our everyday products. Most scientists believe that the carbon dioxide produced by humans is causing the Earth to slowly warm up. We call this global warming and it is caused by the greenhouse effect. Carbon dioxide is one of the many greenhouse gases that trap heat in the atmosphere. This slowly raises the average temperature of the planet. If this warming continues, we may eventually reach a point where the effect is not reversible. Temperatures will rise to such an extent that all life on Earth, apart from extremophiles, will become extinct.

Under normal circumstances, there is only a small amount of carbon dioxide in the air. Most is locked away as hydrocarbon molecules in fossil fuels or as the carbonate ion in limestone, chalk and other 'carbonate' rocks. Carbon dioxide is taken from the air by photosynthesis and returned to the air by respiration. But burning large amounts of fossil fuels or making large quantities of cement 'unlocks' the carbon dioxide that was stored away millions of years in the past. This puts extra carbon dioxide into the air and so there is more than can be removed by photosynthesis. The situation is not helped by large scale felling of trees, the largest photosynthesisers, such as is happening in the tropical rainforests.

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  1. Liquid carbon dioxide does not conduct electricity. What might this tell us about it?
    Covalently bonded compounds do not conduct electricity
  2. Which of the following diagrams best represents a molecule of carbon dioxide?
    The carbon atom is joined to two oxygen atoms by double covalent bonds
  3. What do the lines represent on covalent bonding diagrams, such as in question 2?
    In covalent bonding, pairs of electrons are shared
  4. Which one of the following reactions would produce carbon dioxide?
    A key reaction that you are expected to know is that strong acids will react with metal carbonates to produce water, a salt and carbon dioxide
  5. Choose the correct words in the correct order that would fill the gaps:

    There is a natural and balanced ___________ of carbon dioxide between the __________ and the biosphere. Plants remove it by the process of __________. Animals (and plants during the night) return carbon dioxide to the air by the process of __________.
    This is part of the carbon cycle
  6. Which of the following human activities increase the natural concentration of carbon dioxide in the air?
    There are other activities too. Exams will test you to find out if you realise that any activity that involves burning a fossil fuel or heating limestone will put extra carbon dioxide into the air
  7. Which of the following environmental issues is strongly linked to higher than normal levels of carbon dioxide in the atmosphere?
    The hole in the ozone layer is linked to chloro fluoro carbons (CFC's) and pollution covers a lot more than just the carbon dioxide issue
  8. What is the test for carbon dioxide and what result would you get?
    Whilst moist pH paper would show an orange colour if it was in contact with carbon dioxide dissolved in water, many other things would cause the same result
  9. What is the compound produced in the test for carbon dioxide?
    Limewater is a solution of calcium hydroxide, which is a base. Carbon dioxide is a weak acid and reacts with it to produce the calcium carbonate. Calcium carbonate is insoluble in an alkaline solution and water and so is precipitated, giving the cloudiness
  10. It is thought that the Earth's early atmosphere was mainly carbon dioxide. But where do most scientists believe it came from and which other gases are thought to have been present in small quantities?
    Oxygen only appeared when organisms like blue-green algae had evolved, as they were the first organisms that used photosynthesis

Author: Kev Woodward

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