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Class 9 Science Chapter 13 Carbon: An, Important Element Textbook Questions and, , Answers, , 1. Select the proper option and complete the, statements, (single, all, double, ionic, carbon, give and take,, , hydrogen, multiple, share, most, covalent), , a. A carbon atom forms a.................. bond with, , , , other atoms. In this bond the two atoms, ...electrons., Answer:, , covalent, share, , MaharashtraBoardSolutions.com, , b. All the carbon bonds in a saturated, hydrocarbon ................... electrons., Answer:, , share, , c. At least one carbon bond in an unsaturated, hydrocarbon is .........ccee +, Answer:, , multiple, , dz ou... IS the essential element in all the, organic compounds., Answer:, , Carbon, , e. The element hydrogen is present in......, organic compound., Answer:, , all
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2. Answer the following questions, , a. Why are carbon and its compounds used as, , fuels?, , Answer:, , (i) The name ‘carbon’ is derived from Latin word, ‘carbo’meaning coal. In the earth's crust, carbon, is present to an extent of approximately 0.27%, in the form of carbonate, coal and petroleum., One of the non-crystalline and amorphous form, , of carbon is coal. Coal is a fossil fuel., , (ii) Peat, lignite, bituminous and anthracite are, the four types of coal in the increasing order of, their carbon content and heat produced, respectively. Charcoal and coke are the other, , amorphous forms of carbon used as fuel., , (iii) Compounds of carbon such as, hydrocarbons consist of carbon and hydrogen, and they are easily combustible. For example,, methane (CHa) which occurs in natural gas is, highly inflammable. It bums by reacting with, oxygen to give a bluish flame. In this reaction,, 213 Kceal/mol of heat is given out. Methane, , bums completely., , Chemical reaction:, CHg + 202 > COz2 + 2H20 + Heat, , (iv) Thus when hydrocarbons are burnt in air,, large amount of heat is evolved with formation, of carbon dioxide (CO) and water (H20). Due to, evolution of heat on combustion, carbon and its, , compounds are used as fuels.
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b. In which compound forms does carbon, , occur?, Answer:, , Carbon in its combined state exists as various, , compounds such as:, , ¢ Carbon dioxide and in the form of, carbonates such as calcium carbonate,, marble, calamine (ZnCO3)., , e Fossil fuel — coal, petroleum, natural gas., , e Carbonaceous nutrients — carbohydrates,, proteins, fats., , ¢ Natural fibres — cotton, wool, silk., , e Hydrocarbons — compound of carbon and, , hydrogen.
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c. Write the uses of the diamond., Answer:, , Uses of diamonds are:, , ¢ Diamonds are used in glass cutting and, rock drilling machines., , ¢ Diamonds are used in ornaments., , ¢ Diamond knives are used in the eye, surgery., , ¢ Diamond dust is used for polishing other, diamonds., , ¢ Diamond is used to make windows giving, protection from radiation in space and in, , artificial satellites.
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3. Explain the difference:, , a. Diamond and graphite., , Answer:, , Diamond, , (i) Diamond is a, brilliant, hard and, crystalline allotrope of, , carbon., , (ii) In diamonds, every, carbon atom is, , bonded to four, neighbouring atoms, by covalent bonds, forming tetragonal, three dimensional, structure which, , makes it very hard., , (iii) Density of, diamond is 3.5 g/cm?., , (iv) Diamond is a bad, conductor of, electricity as it does, not have free, , electrons., , Graphite, , (i) Graphite is a black,, soft, brittle and slippery, crystalline allotrope of, , carbon., , (ii) In graphite, every, carbon atom is bonded, to three other carbon, atoms by covalent bonds, in such a way that a, hexagonal layered, structure is formed. A, graphite crystal is made, of many such layers of, carbon atoms. These, layers slip over each, other on applying, , pressure., , (iii) Density of graphite is, 1.9 to 2.3 g/cm?., , (iv) Inside each layer of, graphite, free electrons, move continuously, within the entire layer., Hence, graphite is a good, , conductor of electricity.
