VIEWS: 3 PAGES: 20 POSTED ON: 11/12/2013
FOCUS 5.8 PROPERTIES AND USES OF AIR THE COMPOSITION OF AIR The air is a mixture of gases, as follows: 78% Nitrogen 21% Oxygen 0.03% Carbon dioxide 0.97 % Other gases (noble gases, water vapour, methane gas, nitrous oxide, carbon monoxide) CHEMICAL PROPERTIES OF AIR OXYGEN Theoxygen in the air reacts with other substances in a process called oxidation. Thepollutants in the atmosphere may cause harm to people or the environment. WHEN MAGNESIUM BURNS IN AIR IT USES UP OXYGEN RUSTING IS A CHEMICAL PROCESS THAT OCCURS WHEN WET IRON COMES IN CONTACT WITH OXYGEN RUSTING CAN BE PREVENTED BY THE INTRODUCTION OF A BARRIER BETWEEN IRON AND THE OXYGEN IN THE AIR CARBON DIOXIDE The carbon dioxide is used by plants to make sugar by the process of photosynthesis. Itprovides food and replaces the oxygen gas in the air. POLLUTANTS IN OUR ATMOSPHERE INCLUDE GASES AND AEROSOLS AND CAN IRRITATE YOUR RESPIRATORY SYSTEM. THE INCREASE IN CARBON DIOXIDE IN THE ATMOSPHERE COMES FROM MANY SOURCES, INCLUDING RESPIRATION, FERMENTATION, COMBUSTION AND MANY DIFFERENT INDUSTRIAL PROCESSES. PHYSICAL PROPERTIES OF AIR Airis elastic. This property of air is used to drive machines known as pneumatic devices. THE ENERGY IN MOVING AIR CAN BE USED TO PRODUCE ELECTRICITY. HEATED AIR EXPANDS AND BECOMES LESS DENSE. A PROPANE GAS BURNER IS USED TO HEAT THE AIR IN A HOT AIR BALLOON CAUSING IT TO RISE. AS THE AIR IN THE BALLOON COOLS IT WILL BECOME MORE DENSE AND THE BALLOON WILL FALL. AIR IS A VERY GOOD INSULATOR AGAINST HEAT, COLD AND NOISE. AIR 1 Air is a mixture and not a compound because the different components of air are not chemically combined and can be separated using physical methods (air can be separated into its components using fractional distillation). 2 a Nitrogen is the most abundant gas in the atmosphere. • b Carbon dioxide is the gas used by green plants in the process of photosynthesis and the best known greenhouse gas. • c Oxygen is the gas used by all living things in the process of chemical respiration. 3 Air is only 20 per cent oxygen gas, so a flame will not burn as brightly as it would in pure oxygen. 4. A coating of paint or plastic prevents oxygen and moisture getting to the surface of the metal, thus reducing corrosion. 5. Three gases that contribute to air pollution are nitrogen dioxide, sulfur dioxide and carbon dioxide. 6 ‘Air is a real substance’ means that air takes up space and has mass. This can be proved in a number of ways: • You can find the mass of a basketball before pumping it up and comparing it to the mass after pumping it up. The increase in mass is due to the air that is now inside it. • You can try filling a conical flask with water through a funnel that is sealed around the neck. The water will not enter the conical flask as the air cannot escape. 7. Useful applications—powering an electrical generator, windmills, moving a yacht. Non-useful applications—storms, hurricanes, tornadoes, wind resistance of moving cars. 8 The elastic nature of air refers to the fact that if the air in a vessel is compressed, when the force is removed or released the air will expand back to its original shape within the container. This property is used in tyres and other air- operated tools such as a jack hammer. 9. As air is heated it expands and becomes less dense than the cooler air that surrounds the balloon. The less dense air of the hot-air balloon floats on the cooler air, so it rises. As the air in the balloon cools it becomes more dense and falls. The height of the balloon can be controlled by using a gas burner to heat the air as required. 10 If a jumper is baggy it traps a layer of air between your body and the jumper. As air is an insulator it reduces the amount of heat that is lost to the environment, keeping you warmer. • 11 If the ball has a split or a hole in it the air escapes from the ball when it hits the ground. If the ball is in good condition the elastic nature of air means that the ball can become distorted when it hits the ground but return the ball to its original shape as it leaves the ground. This helps the ball bounce back towards its original height (as some energy is lost, it will not return to its original height). • 12 Ozone is considered to be a pollutant when it is produced at altitudes closer to the surface. It is a respiratory irritant when breathed by humans. At higher altitudes ozone is essential in providing protection from UV radiation, which can cause sunburn and even cancer in high doses. • 13 The concept map shows that there are a large number of sources of carbon dioxide, including industrial processes, fermentation, cellular respiration and burning. The carbon dioxide produced in these processes is consumed by plants in the process of photosynthesis. It is this balance between production and use that is essential in maintaining the balance between oxygen and carbon dioxide in our environment. • 14 A 100 per cent oxygen environment is potentially very dangerous, as any fire will burn much brighter and more rapidly because of the high concentration of oxygen. By switching to a 60 per cent oxygen mixture, the rate of burning is reduced, which means that any fires will not burn as brightly or as rapidly and can be controlled more easily.
Pages to are hidden for
"FOCUS 5.8 PROPERTIES AND USES OF AIR"Please download to view full document