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| Alkenes - Ethene, A Typical Example |
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| Molecular formula: C2H4 |
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| Structure: |
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| Common name: Ethylene |
| Ethene is an unsaturated hydrocarbon with
a double bond. |
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| Ethene is prepared by cracking of higher alkanes as follows: |
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| Ethene is prepared by thermal cracking of hexane. |
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| Principle |
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| Thermal cracking of kerosene. |
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| Procedure |
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 Sand soaked with kerosene is taken in hard glass test tube. |
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 The test tube is clamped horizontally to a clamp stand |
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 Broken pumice is placed at the other end of the test tube. |
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 The apparatus is assembled as shown in the figure. |
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 The burner is lighted and the test tube is heated strongly. Pumice and sand are heated alternately. |
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 Thermal cracking of kerosene vapours takes place in the pores of pumice to liberate ethene gas. |
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| Laboratory Preparation of Ethene |
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| Mode of collection |
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| Ethene gas formed is collected by the downward displacement of water. |
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| Physical properties |
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| Ethene is a colourless gas with a sweetish odour. It is insoluble in water and soluble in organic solvents. It causes unconsciousness when inhaled. |
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| Chemical properties |
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 Combustion |
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| Ethene burns in air with a sooty flame to give carbon dioxide,water vapour and heat. A sooty flame is produced because ethene is an unsaturated compound having a higher percentage of carbon than hydrogen (unlike saturated compounds). |
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 Addition reactions |
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| Ethene being an unsaturated compound, undergoes addition reactions to form saturated compounds. |
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| a. With chlorine -Chlorination |
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| Reaction takes place to form dichloro ethane. |
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| b. With bromine - Bromination |
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| Reaction takes place to form dibromo ethane |
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| Dibromo ethane |
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| c. With hydrogen - Hydrogenation |
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| Reaction takes place to form ethane. |
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| Ethane |
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| d. With Hydrochloric acid |
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| Reaction takes place to form mono chloroethane. |
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| e. Polymerisation |
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| Ethene undergoes addition polymerisation with itself at 200oC and 2000 atmospheres of pressure to form polythene. |
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| f. Reaction with water - Hydration |
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| Reaction takes place to form ethyl alcohol in the presence of phosphoric acid, a catalyst. |
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 In the manufacture of ethyl alcohol and ethylene glycol which are used as important starting materials in the manufacture of synthetic fibres. |
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 Manufacture of plastics like polythene. |
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 In artificial ripening of fruits like bananas, apples and oranges. |
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