Air Online Test 8th Science Lesson 11 Questions in English

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Air is a mixture of gases that surrounds our planet earth. It is essential for the survival of all the living things.

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Air contains 78.09% of nitrogen.

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Air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide and small number of other gases. We breath in oxygen and breath out carbon dioxide.

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Plants in turn use carbon dioxide for photosynthesis and release oxygen into the atmosphere. Since men have been cutting down trees for their needs, the amount of carbon dioxide in the atmosphere is increasing. This is responsible for the raising of atmospheric temperature

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Industries and vehicles release gases like carbon monoxide and sulphur dioxide into the atmosphere. This has resulted in effects like global warming and acid rain which affect us in many ways. In total, the quality of air is gone in the modern days.

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All living things in the world need oxygen. We cannot imagine the world without oxygen. Swedish chemist C.W. Scheele first discovered oxygen in 1772. He called the gas fire air or vital life because it was found to support the process of burning.

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Oxygen was independently discovered by the British scientist Joseph Priestley in 1774.

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Lavoisier named oxygen. The name oxygen comes from the Greek word ‘oxygenes’ which means ‘acid producer’. It is called so because early chemists thought that oxygen is necessary for all acids.

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Oxygen is the third most abundant element after Hydrogen and Helium in the universe. It occurs both in free state and combined state.

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Oxygen is present in free state as dioxygen molecule (O2) in the atmosphere. Most of this has been produced by the process photosynthesis in which the chlorophyll present in the leaves of plants uses solar energy to produce glucose.

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In combined state it is present in the earth’s crust as silicates and metal oxides. It is also found in the water on the surface of the earth.

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Oxygen in free state in Atmospheric air is 21 % and in water is 88 – 90 %.

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Oxygen is a poor conductor of heat and electricity.

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Oxygen can be made into liquid (liquified) at high pressure and low temperature.

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Hydrocarbons (compound containing C and H) react with oxygen to form carbon dioxide and water vapour. E.g Wood, Petrol, Diesel, LPG, etc. When they burn in oxygen, they produce heat and light energy. Hence, they serve as fuel.

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The process of conversion of iron into its hydrated form of oxide in the presence of air and moisture (humid atmosphere) is called rusting. Rust is hydrated ferric oxide.

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Oxygen is used to remove carbon impurities from steel. It is used to oxidize rocket fuel. It is used for artificial respiration by scuba divers, mountaineers, astronauts, patients etc.

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Nitrogen is one of the most important elements. Animals and plants need nitrogen for their growth. All living organisms (including us) contain nitrogen. It is an essential element present in proteins and nucleic acids which are the ‘building blocks’ of all living things.

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Nitrogen was first isolated from the air by Swedish chemist Carl Wilhelm Scheele in 1772. The name ‘nitrogen’ is derived from the Greek words ‘nitron’ and ‘gene’ meaning ‘I produce nitre’. Nitre is potassium nitrate compound of nitrogen.

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Antoine Lavoisier suggested the name azote, from the Greek word meaning ‘no life’.

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Oxygen is the most abundant element on the earth by mass.

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Nitrogen is the fourth most abundant element in the human body by mass. It accounts for about three percent of the mass of the human body. It is thought to be the seventh most abundant element in the universe by mass.

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Titan, the largest moon of Saturn, has an atmosphere made up of 98% Nitrogen.

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Nitrogen occurs both in free state and combined state. Nitrogen exists in free state in the atmospheric air as dinitrogen (N2). It is present in volcanic gases and gases evolved by burning of coal.

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Nitrogen is slightly lighter than air. When it freezes, it becomes a white solid. It is neutral to litmus like oxygen.

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The plants require soluble compounds of nitrogen. Thus, plants depend on other processes to supply them with nitrates. Any process that converts nitrogen in the air into a useful nitrogen compound is called nitrogen fixation. Fixation of nitrogen is carried out both naturally and by man.

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Liquid nitrogen is used as a refrigerant.

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Many explosives such as TNT (Trinitrotoluene), nitro-glycerine, and gun powder contain nitrogen. It is used for the preservation of fresh foods, manufacturing of stainless steel, reducing fire hazards, and as part of the gas in incandescent light bulbs.

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Nitrogen is inactive at ordinary conditions. It combines with many elements at high temperature and pressure or in the presence of catalyst. Nitrogen is neither combustible nor a supporter of combustion. So, nitrogen in the air moderates the rate of combustion.

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Carbon dioxide is present in air to the extent of about 0.03% in volume. It is evolved by the plants and animals during respiration and is produced during fermentation reactions.

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Much of the naturally occurring CO2 is emitted from the magma through volcanoes. CO2 may also originate from the bio degradation of oil and gases. When carbon dioxide accumulates more in the atmosphere it produces harmful effects.

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The process of conversion of solid into vapour without reaching liquid state is called sublimation.

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Carbon dioxide fairly soluble in water and turns blue litmus slightly red. So, it is acidic in nature. Carbon dioxide is non-combustible and not a supporter of combustion.

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Aerated water is nothing but carbon dioxide dissolved in water under pressure. This is also called ‘soda water’.

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The solar radiation is absorbed by the surface of land and ocean. In turn, they release infra-red radiation or heat into the atmosphere. Certain gaseous molecules present in the atmosphere absorb the infra-red rays and reradiate the heat in all directions. Hence, these gases maintain the temperature of earth’s surface. The gases which absorb these radiations are called greenhouse gases and this effect is called greenhouse effect.

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The greenhouse gases are CO2, N2O, CH4, CFC (Chloro-Fluro carbon) etc. The increase in the levels of these gases results in the gradual increase of temperature of the earth’s surface.

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The increased greenhouse effect is caused due to increase in the air pollutants and it results in the average increase of temperature of the atmosphere. This is called as Global warming.

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Increase in frequency of floods, soil erosion and unseasonal rains.

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In order to save the earth and its resources we need to take certain measures. Some of the measures are given below. 1. Reduction in the use of fossil fuels. 2. Controlling deforestation. 3. Restricting the use of CFCs. 4. Planting more trees. 5. Reducing, reusing and recycling resources.

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Rain water is actually the purest form of water. However, pollutants such as oxides of nitrogen and sulphur in the air released by factories, burning fossil fuels, eruption of volcanoes etc., dissolve in rain water and form nitric acid and sulphuric acid which adds up to the acidity of rain water. Hence, it results in acid rain.

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Acid rain inhibits germination and growth of seedlings.

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Using non-conventional source of energy.

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Bacteria convert atmospheric nitrogen directly into soluble nitrogen compounds.