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| Question | Answer |
| What is clean air made up of? | Clean air is made up of 78% nitrogen, 21% oxygen and of the remaining 1% only 0.035% is carbon dioxide. |
| Why do these percentages change very little? | These percentage change very little because there is a balance between the processes that use up and make both carbon dioxide and oxygen. |
| Some of these processes are shown in the carbon cycle. Draw the carbon cycle. | |
| Over the last few centuries the percentage of carbon dioxide in air has increased slightly due to a number of factors. Name two of these factors and why they have contributed to this increase. | - Deforestation ~ as more rainforests are cut down, less photosynthesis takes place - Increased population ~ as populations increase, the world's energy requirements increase. |
| What formed the original atmosphere? | Gases escaping from the interior of the Earth formed the original atmosphere. |
| What did plants that could photosynthesise do? | Plants that could photosynthesise removed carbon dioxide from the atmosphere and added oxygen. Eventually the amount of oxygen reached its current level. |
| Where do gases come from? | Gases come from the centre of the Earth through volcanoes in a process called degassing. |
| What do scientists do to form theories about the original atmosphere? | Scientists analyse the composition of these gases to form theories about the original atmosphere. |
| Describe one theory about the Earth's early atmosphere. | One theory is that the atmosphere was originally rich in water vapour and carbon dioxide. This vapour condensed to form oceans and the carbon dioxide dissolved in the water. The percentage of nitrogen slowly increase and, being unreactive, little nitrogen was removed. Over time, organisms that could photosynthesise evolved and converted carbon dioxide and water into oxygen. As the percentage of oxygen in the atmosphere increased, the percentage of carbon dioxide decreased, until today's levels were reached. |
| Why is it important to control atmospheric pollution? | It is important to control atmospheric pollution because of the effects it can have on people's health, the natural environment and the built environment. |
| Sulfur dioxide is a pollutant. What can sulfur dioxide cause? | Sulfur dioxide is a pollutant and can cause difficulties for people with asthma. It can also dissolve in water to form acid rain that damages wildlife and limestone buildings. |
| A car is fitted with a catalytic converter. What is a catalytic converter? | A catalytic converter is a box fitted to vehicle exhausts which reduce the level of nitrogen oxides and unburnt hydrocarbons in the exhaust fumes. |
| What does a car fitted with a catalytic converter do? | A car fitted with a catalytic converter changes carbon monoxide into carbon dioxide. |
| In a catalytic converter what reaction takes places on the surface of the catalyst? | In a catalytic converter, a reaction between nitric oxide and carbon monoxide takes place on the surface of the catalyst. |
| Which two gases are formed in this reaction? | The two gases formed are natural components of air - nitrogen and carbon dioxide. |
| Write the balanced symbol equation for the reaction between nitric oxide and carbon monoxide which takes place in a catalytic converter. | 2CO + 2NO > N2 + 2CO2 |
| What is a catalyst? | A catalyst is a chemical that speeds up a reaction but is not changed or used up by the reaction. |
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