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Std VII QI Allotropy of Carbons Choose the correct answer 1. The structure of diamond is tetrahedral. 2. Diamond is used as a gem stone , because it is a giant crystal. 3. Graphite is used as electrodes in dry cells, because it is a good conductor of electricity. 4. Coke is a good fuel , because it burns without smoke. 5. The allotrope of carbon consisting of discrete molecules is fullerene. 6. Substances obtained when coal is subjected to destructive distillation are coal tar and coke. 7. Charcoal floats on water , because it is porous. 8. Allotropy is caused due to the difference in arrangement of atoms. 9. The gas which turns lime water milky is carbon dioxide. 10. The compound of carbon which is used in the manufacture of cement is calcium carbonate. 11. The chemical name of baking soda is sodium bicarbonate. Q II Match the following A 1. Bone charcoal 2. Gas carbon B a) decolourization of sugar b) the deposites formed on the roofs of the retorts during destructive distillation of coal 3. Diamond c) glass cutting instrument 4. Fullerene d) yellow spherical ball 5. Coal e) formed by slow decomposition of plants. Q III 1. State true or false. If false give reason Coke reacts with metal oxides to give metals. Yes. 2. Fullerene cannot be used as lubricants. False. Fullerenes are bucky (spherical) balls, the balls can roll between the surfaces. so fullerene is wonderful lubricant . 3. Coal gas is obtained when coal is subjected to destructive distillation. True. 4. Sugar charcoal consists of a lot of carbon compounds as impurities. False. Because sugar charcoal is the purest form of amorphous carbon. 5. Gas carbon is a bad conductor of electricity. False . It is a good conductor of electricity , so it is used in making electrodes. Q IV 1. Answer the following What is allotropy? Name the allotropic forms of carbon . Mention one use of each. An s. An element can exist in more than one form. This phenomenon is called allotropy. The allotropic forms of carbon are diamond , graphite, fullerene, charcoal, coke, coal, gas carbon, and lampblack. Diamond—Used in the tools of cutting glasses and drilling rocks Graphite---Graphite is mixed with little amount of clay and used as pencil lead. Fullerene---Used as lubricants in electronic devices. Charcoal---Charcoal is used as a fuel. Coal ---Coal is used as fuel in thermal power plants and in steam engines Coke---coke is used in the extraction of iron from its ore. Gas carbon—It is used in making electrodes. Lampblack---It is used in the manufacture of printing ink, black paint, Indian ink and shoe polish. 2. Explain the preparation of wood charcoal, with the help of a neat labelled diagram. Ans. Take a hard glass test tube. Put some wood shavings into it. Close the mouth with one holed rubber stopper. Then connect it to another test tube as shown in the figure. For figure refer page no. 164 fig 10.10 Heat the hard glass test tube filled with wood shavings. We get charcoal as residue in it. Wood tar and a mixture of organic compounds are obtained in another test tube. 3. What are the uses of charcoal.? Ans. Uses of charcoal 1) It is used as a fuel. 2) It is used in the manufacture of gun power. 3) Activated charcoal is used in the gas masks and in purification of water 4. What are the uses of coal ? Ans. Uses of coal 1) Coal is used as fuel in thermal power plants and in steam engines. 2)It is used in the manufacture of coal gas , coal tar, and coke 3) It is used in the manufacture of fuel gases like water gas and producer gas 5. Which allotropy of carbon is used in the manufacture of black paint ? Ans. Lampblack is used in the manufacture of black paint. 6. How coke is obtained ? Ans. When coal is subjected to destructive distillation, coke is obtained as a residue. 7. State any two uses of fullerene ? Ans. Uses of fullerene 1) It is used as lubricants. 2) Fullerene are used in T.V picture tubes 8. How is calcium carbonate prepared in the laboratory ? Ans. Calcium carbonate is formed by the reaction of carbonic acid with calcium hydroxide. Carbonic acid is formed when carbon dioxide dissolve in water. Carbon dioxide + water →Carbonic acid Carbonic acid + Calcium hydroxide → Calcium carbonate +water 9. Write any one use of the following Calcium carbonate , Sodium carbonate, Sodium bicarbonate Ans. Calcium carbonate___It is used in the manufacture of cement and glass. Sodium carbonate____It is used in softening hard water. Sodium bicarbonate____It is used in the manufacture of baking powder. Allotropy of Oxygen QI 1. Answer the following Name the allotropic forms of oxygen. Ans. 2. Allotropic forms of oxygen are diatomic molecule and tri-atomic molecule. What are the properties of oxygen ? Ans. Properties of oxygen 1) Oxygen reacts with other elements to give the respective oxides. 2)It react with some compounds and decomposes them. 3. What is ozone ? state its properties. Ans. Ozone is a light bluish gas found in the upper layer of the atmosphere. Properties of ozone are 1) ozone is a poisonous gas with fishy smell. 2) it causes respiratory problems, if inhaled. 3) it damages plants and trees, if comes in contact with them. 4) it causes damages to automobile tyres and asphalt, if reacts with them. 4. How does ozone layer protect the living organisms on the earth? Ans. Ozone layer prevents ultraviolet rays coming from the sun and thus prevents them to reach the earth. Thus it protects the life on the earth from harmful effects of U.V rays. 5 What is depletion of ozone layer? Ans. The decrease in the quantity of ozone in the upper layer of the atmosphere is called depletion of ozone layer. 6. What are the causes for the depletion of ozone layer? Ans. Pollutants like oxides of nitrogen and chlorofluoro carbon are the causes for the depletion of ozone layer. 7. Suggest some measures to prevent the depletion of ozone layer. Ans. Control of air pollution will save the ozone layer.