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Alkenes
Reactions of Carbon Compounds
| Question | Answer |
|---|---|
| Functional group of alkenes | C=C double bond |
| Alkene end with the letters | ene |
| General formula for alkene homologous series. | CnH2n |
| T or F. All alkenes are unsaturated compounds. | T |
| How many carbon atoms must be present for an alkene to have structural isomers? | 4 or more carbons are required. Structural isomers results from 1) change in the position of the functional group (double bond) 2) branching of the molecule. |
| T or F. When numbering the carbons of an alkene, it should be numbered such that the double bond gets the lowest number possible. | T |
| Name CH3CH2CHCH=CH2 | pent-1-ene or 1-pentene |
| Name CH3CH2C(CH3)CHC=CH2 | 3-methylpent-1-ene |
| Name CH3CH2=C(CH3)CH2 | 2-methylbut-2-ene |
| Alkene + oxygen --> | carbon dioxide (g) + water (g) |
| Why do alkenes burn with a smoky flame? | They have a higher ration of carbon to hydrogen atoms. When they burn, they release unreacted carbon as soot and sometimes carbon monoxide in addition to carbon dioxide and steam. |
| What happens in an addition reaction? | Extra atoms are added to alkene molecules and one bond in the double bond is broken in the process. No hydrogen molecules are lost. The result is the formation of a saturated compound (alkenes become alkanes) |
| If hydrogen is added to an alkene in an addition reaction, the process is called | hydrogenation |
| What conditions are required for hydrogenation of an alkene? | Ni catalyst, 5 atm , 150 degrees C |
| C2H4 (g) + H2 (g) --> (Ni catalyst, 5 atm, 150 degrees C above arrow) | C2H6 (g) |
| How many different products are always formed from addition reactions? | One |
| If a halogen is added to an alkene in an addition reaction, the process is called | halogenation |
| The product of halogenation reactions is called a | haloalkane |
| What conditions are required for halogenation of an alkene? | None. Simply add halogen to alkene and reaction will occur rapidly. |
| C3H6 (g) + Br2 (g) --> | C3H6Br2 (l) |
| Alkene + hydrogen halide --> | haloalkane |
| C2H4 (g) + HCl (g) --> | C22H5Cl (l) |
| What is a haloalkane/alkyl halide? | An alkane with one or more hydrogen replaced with a halogen atom. |
| If water is added to an alkene in an addition reaction, the process is called | hydration |
| What conditions are required for hydration of an alkene to occur? | H3PO4 in silica; 60-70 atm ; 300 degrees C (This is the process used in the industrial preparation of ethanol from ethene) |
| Alkene + oxidising agent [O] --> | dialcohol (diol) |
| Ethene + KMnO4 --> | ethane-1,2-diol |
| C2H4 (g) + H20 (l) + [O] --> | C2H4(OH)2(l) |
| Positive test for ALKANES using KMnO4 will give this result | Solution remains purple since alkanes fo not react with oxidising agents. |
| Positive test for ALKENES using KMnO4 will give this result | Solution changes colour rapidly from purple to colourless since alkenes rapidly reduce the purple MnO4 superscipt - ions to colourless Mn superscript 2+ ions |
| Positive test for ALKANES using bromine solution will give this result | Solution remains red-brown since alkanes do not react with bromine under standard lab conditions. |
| Positive test for ALKENES using bromine solution will give this result | Solution changes rapidly from red-brown to colourless since alkenes undergo rapid addition reaction with bromine solution, under any conditions, including darkness. |
| What are alkenes extremely useful as starting materials in manufacturing other chemicals? | They undergo a wide range of reactions (e.g. addition reactions and polymerization) due to the presence of carbon-carbon double bonds. |
Created by:
Ms. Kumar
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