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 covalent bond with other atoms. In this bond the two atoms share electrons.
*(b) All the carbon bonds in a saturated hydrocarbon share electron.
*(c) At least one carbon bond in an unsaturated hydrocarbon has multiple bond.
(d) Carbon is the essential element in all the organic compounds.
*(e) The element hydrogen is present in all organic compound.
2. Answer the following questions
(a) Why are carbon and its compounds used as fuels?
Ans. Fuels are classified on the basis of their physical state as follows :
Solid fuels : Wood – Cellulose (C6H10O5)n, Coal – carbon, Coke – carbon
Liquid fuels : Kerosene – carbon, ethanol – carbon, petrol, diesel – carbon
Gaseous fuels: Methane-carbon, liquefied petroleum gas (LPG) – butane – isobutane, natural gas – methane, water gas – (CO + H2), producer gas – CO. Above all fuels are combustible carbon compounds and contain combustible carbon, therefore, carbon and its compounds are used as fuels.
(b) In which compound forms does carbon occur?
Ans. In the combined state carbon occurs in the following compounds : (1) Carbon dioxide from air, in the form of carbonates such as calcium carbonate, marble and calamine (ZnC03). (2) Fossil fuels. Examples : Coal, petroleum, biogas and natural gas. (3) Carbonaceous nutrients, examples: carbohydrates, proteins, fats. (4) Natural fibres, examples : cotton, wool, silk. etc.
(c) Write the uses of diamond.
Ans. (1) Diamonds are used in glass cutting and rock drilling machines. (2) It is used as precious stones in ornaments. (3) Diamond knives are used for eye surgery. (4) In artificial satellites, diamonds are used to make windows giving protection from radiation in space.
3. Explain the difference:
(a) Diamond and graphite.
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(b) Crystalline and non-crystalline forms of carbon.
Ans.
4. Write scientific reasons
(a) Graphite is a conductor of electricity.
Ans. (1) Graphite is a soft, greyish black crystalline allotrope of carbon. In graphite, each carbon atom is attached to three other carbon atoms forming a hexagonal planar structure. (2) In graphite, free electrons move throughout the entire hexagonal layers and hence, graphite is a good conductor of electricity.
(b) Graphite is not used in ornaments.
Ans. (1) In natural form graphite is a soft, greyish black and slippery. (2) While making ornaments hard metals are used. Since graphite is not hard substance it cannot be used in ornaments.
(c) Limewater turns milky when CO2 is passed through it.
Ans. When C02 is passed through fresh lime water, white precipitate of calcium carbonate is formed due to which lime water turns milky.
(d) Biogas is an eco-friendly fuel.
Ans. (1) Biogas contains about 55% to 60% methane and the rest is carbon dioxide. (2) Biogas is a very cheap fuel, which meets the demand for cooking gas. (3) Biogas burns almost instantaneously to provide heat quickly. (4) The combustion of biogas can be easily controlled. (5) It does not produce any solid waste products. (6) It can be transported easily and can be supplied through pipes to limited distant place. (7) It has high heat content, hence biogas is an eco-friendly fuel.
5. Explain the following.
(a) Diamond, graphite and fullerenes are crystalline forms of carbon.
Ans. (1) A crystalline form of carbon has a regular and definite arrangement of atoms. (2) In diamond, each carbon atom is linked to four other carbon atoms by covalent bonds. Therefore, diamond has tetragonal three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in such a way that a hexagonal layered structure is formed. In fullerene, C60 atoms are joined to each other in pentagonal and hexagonal arrangements. (3) Since diamond, graphite and fullerene have definite shape, sharp edges and plane surfaces, they are in crystalline form.
(b) Methane is called marsh gas.
Ans. Methane is formed by the decomposition of plants and animal matter at the surface of marshy lands. Hence, methane is called marsh gas.
(c) Petrol, diesel, coal are fossil fuels.
Ans. Millions of years ago the remains of plants and animals got buried under the earth. Due to action of microorganisms, the gaseous substances in these remains were released into atmosphere and what was left behind were energy rich carbon compounds. After this, under tremendous pressure, the liquid substances in these compounds drained away as petroleum, which on fractional distillation yields petrol and diesel, and the remaining mineral solidified into compact and hard rock and this material is called coal. Therefore, petrol, diesel, coal are fossil fuels.
(d) Uses of various allotropes of carbon.
Ans. Diamonds: (1) Diamonds are used in glass cutting and rock drilling machines. (2) It is used as precious stones in ornaments. (3) Diamond knives are used for eye surgery.
Graphite: (1) Graphite is used for making lubricants. (2) It is used for making carbon electrodes. (3) Graphite is used in pencils for writing on paper. Fullerenos: (1) Fullerenos are used as insulators. (2) Fullerenes are used as a catalyst in water purification. (3) Fullerene exhibits super conductivity at a certain temperature. Coal : (i) Coal is used as fuel in factories and homes, (ii) Coal is used to obtain coke, coal gas and coal lar. (iii) Coal is used in thermal power plants for generation of electricity.
(e) Use of CO2 in fire extinguisher.
Ans. Carbon dioxide neither burns nor supports burning. (1) It is not poisonous. (2) It is heavier than air. (3) When it is spread on a burning object, it covers the object and separates it from air. Thus, the fire is extinguished. Hence, carbon dioxide is used in fire extinguisher for extinguishing fires.
(f) Practical uses of CO2.
Ans. (1) Carbon dioxide is used in the manufacture of aerated drinks. (2) Solid carbon dioxide is used in cold storage and also keep milk and milk products and frozen substances cool during transport. It is used for getting special effects of a mist in dramas and movies. (3) Carbon dioxide obtained by chemical reaction or kept under pressure is used in fire extinguisher. (4) Liquefied C02 is used to remove caffeine from coffee. (5) Liquefied C02 is used as solvent in dry cleaning.
6. Write two physical properties each.
(a) Diamond
Ans. (1) Pure diamond is the hardest known substance. (2) The melting point of diamond is 3500 °C.
(b) Charcoal
Ans. (1) Charcoal contains some volatile compounds. (2) It burns with smoke.
(c) Fullerene
Ans. (1) Fullerenes are soluble in carbon disulphide and chlorobenzene. (2) Fullerenes exhibit super conductivity at a certain temperature.
7. Complete the following Chemical reactions.
Ans.
8. Write answers to the following in detail.
(a) What are the different types of coal? What are their uses?
Ans. (1) Coal is a fossil fuel. It contains carbon, hydrogen and oxygen. It also contains nitrogen, phosphorus and sulphur in small quantity. It occurs in the solid state. (2) Coal is classified on the basis of its carbon content into (i) Peat (less than 60% of carbon) (ii) lignite (60 to 70% of carbon) (iii) bituminous (70 to 90% of carbon) and (iv) anthracite (about 95% of carbon). Depending on the percentage of carbon, the heat generated changes. (3) Uses : (i) Coal is used as fuel in factories and homes, (ii) Coal is used to obtain coke, coal gas and coal tar. (iii) Coal is used in thermal power plants for generation of electricity.
(b) How will you prove experimentally that graphite is good conductor of electricity?
Ans. Apparatus required: Lead pencil, electrical wires, battery/cell, small bulb, etc.
Step-I: Remove the lead from a pencil and assemble the apparatus as shown in the diagram. Step-II: Start the electric current in the circuit, the moment the electric current is passed through the circuit, the bulb glows. This experiment proves that graphite is a good conductor of electricity as graphite has free electrons moving continuously within the entire layer and these free electrons conduct electricity in the lead of the pencil
(c) Explain the properties of carbon.
Ans. (1) Carbon exhibits allotropy. It exists in more than one form. The chemical properties of these different forms are the same but their physical properties are different. (2) Carbon allotropes have two forms : crystalline form and amorphous form. (3) Crystalline forms : (i) It has a regular and definite arrangement of atoms, (ii) They have high melting points and boiling points. (iii) A crystalline form has a definite geometrical shape, sharp edges and plane surfaces, (iv) Carbon has three crystalline allotropes : 1. Diamond 2. Graphite 3. Fullerene. (4) Non-crystalline/Amorphous forms : The arrangement of carbon atoms is irregular. Examples : Coal, charcoal, coke.
(d) Classify carbon.
Ans. Carbon exhibits allotropy and it has two forms : crystalline and amorphous.
1. Crystalline form : Carbon has three cystalline allotropes (i) Diamond (ii) Graphite (iii) Fullerene 2. Amorphous form : Carbon has following amorphous forms : (i) Coal: (1) Peat (2) Lignite (3) Bituminous (4) Anthracite (ii) Charcoal (iii) Coke.