JK-TK/Newdata huggingface dataset:
Ethane + Air -> carbon(IV) oxide + water (excess air/oxygen) 2C2H6(g) + 7O2(g) -> 4CO2(g) + 6H2O(l/g) (b) Ethane when ignited burns with a blue non sooty flame in limited air to form carbon(II) oxide and water. 13 Ethane + Air -> carbon(II) oxide + water (excess air/oxygen) 2C2H6(g) + 5O2(g) -> 4CO(g) + 6H2O(l/g) 3.(a) Propane when ignited burns with a blue non sooty flame in excess air to form carbon(IV) oxide and water. Propane + Air -> carbon(IV) oxide + water (excess air/oxygen) C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(l/g) (b) Ethane when ignited burns with a blue non sooty flame in limited air to form carbon(II) oxide and water. Ethane + Air -> carbon(II) oxide + water (excess air/oxygen) 2C3H8(g) + 7O2(g) -> 6CO(g) + 8H2O(l/g) ii)Substitution Substitution reaction is one in which a hydrogen atom is replaced by a halogen in presence of ultraviolet light. Alkanes react with halogens in presence of ultraviolet light to form halogenoalkanes. During substitution: (i)the halogen molecule is split into free atom/radicals. (ii)one free halogen radical/atoms knock /remove one hydrogen from the alkane leaving an alkyl radical. (iii) the alkyl radical combine with the other free halogen atom/radical to form halogenoalkane. (iv)the chlorine atoms substitute repeatedly in the alkane. Each substitution removes a hydrogen atom from the alkane and form hydrogen halide. (v)substitution stops when all the hydrogen in alkanes are replaced with halogens. Substitution reaction is a highly explosive reaction in presence of sunlight / ultraviolet light that act as catalyst. Examples of substitution reactions Methane has no effect on bromine or chlorine in diffused light/dark.
(v)substitution stops when all the hydrogen in alkanes are replaced with halogens. Substitution reaction is a highly explosive reaction in presence of sunlight / ultraviolet light that act as catalyst. Examples of substitution reactions Methane has no effect on bromine or chlorine in diffused light/dark. In sunlight , a mixture of chlorine and methane explode to form colourless mixture of chloromethane and hydrogen chloride gas. The pale green colour of chlorine gas fades. Chemical equation 1.(a)Methane + chlorine -> Chloromethane + Hydrogen chloride
14 CH4(g) + Cl2(g) -> CH3Cl (g) + HCl (g) H H H C H + Cl Cl -> H C Cl + H Cl H H (b) Chloromethane + chlorine -> dichloromethane + Hydrogen chloride CH3Cl (g) + Cl2(g) -> CH2Cl2 (g) + HCl (g) H H H C Cl + Cl Cl -> H C Cl + H Cl H Cl (c) dichloromethane + chlorine -> trichloromethane + Hydrogen chloride CH2Cl2 (g) + Cl2(g) -> CHCl3 (g) + HCl (g) Cl H H C Cl + Cl Cl -> Cl C Cl + H Cl H Cl (c) trichloromethane + chlorine -> tetrachloromethane + Hydrogen chloride CHCl3 (g) + Cl2(g) -> CCl4 (g) + HCl (g) H Cl Cl C Cl + Cl Cl -> Cl C Cl + H Cl Cl Cl
15 Ethane has no effect on bromine or chlorine in diffused light/dark. In sunlight , a mixture of bromine and ethane explode to form colourless mixture of bromoethane and hydrogen chloride gas. The red/brown colour of bromine gas fades.
Chemical equation 1.(a)Methane + chlorine -> Chloromethane + Hydrogen chloride
14 CH4(g) + Cl2(g) -> CH3Cl (g) + HCl (g) H H H C H + Cl Cl -> H C Cl + H Cl H H (b) Chloromethane + chlorine -> dichloromethane + Hydrogen chloride CH3Cl (g) + Cl2(g) -> CH2Cl2 (g) + HCl (g) H H H C Cl + Cl Cl -> H C Cl + H Cl H Cl (c) dichloromethane + chlorine -> trichloromethane + Hydrogen chloride CH2Cl2 (g) + Cl2(g) -> CHCl3 (g) + HCl (g) Cl H H C Cl + Cl Cl -> Cl C Cl + H Cl H Cl (c) trichloromethane + chlorine -> tetrachloromethane + Hydrogen chloride CHCl3 (g) + Cl2(g) -> CCl4 (g) + HCl (g) H Cl Cl C Cl + Cl Cl -> Cl C Cl + H Cl Cl Cl
15 Ethane has no effect on bromine or chlorine in diffused light/dark. In sunlight , a mixture of bromine and ethane explode to form colourless mixture of bromoethane and hydrogen chloride gas. The red/brown colour of bromine gas fades. Chemical equation (a)Ethane + chlorine -> Chloroethane + Hydrogen chloride CH3CH3(g) + Br2(g) -> CH3CH2Br (g) + HBr (g) H H H H H C C H + Br Br -> H C C H + H Br H H H Br Bromoethane H H H Br H C C H + Br Br -> H C C H + H Br H Br H Br 1,1-dibromoethane H Br H Br H C C H + Br Br -> H C C Br + H Br H Br H Br 1,1,1-tribromoethane H Br H Br H C C Br + Br Br -> H C C Br + H Br H Br Br Br 1,1,1,2-tetrabromoethane H Br H Br H C C Br + Br Br -> Br C C Br + H Br
16 Br Br Br Br 1,1,1,2,2-pentabromoethane H Br Br Br Br C C Br + Br Br -> Br C C Br + H Br Br Br Br Br 1,1,1,2,2,2-hexabromoethane Uses of alkanes 1.Most alkanes are used as fuel e.g.
In sunlight , a mixture of bromine and ethane explode to form colourless mixture of bromoethane and hydrogen chloride gas. The red/brown colour of bromine gas fades. Chemical equation (a)Ethane + chlorine -> Chloroethane + Hydrogen chloride CH3CH3(g) + Br2(g) -> CH3CH2Br (g) + HBr (g) H H H H H C C H + Br Br -> H C C H + H Br H H H Br Bromoethane H H H Br H C C H + Br Br -> H C C H + H Br H Br H Br 1,1-dibromoethane H Br H Br H C C H + Br Br -> H C C Br + H Br H Br H Br 1,1,1-tribromoethane H Br H Br H C C Br + Br Br -> H C C Br + H Br H Br Br Br 1,1,1,2-tetrabromoethane H Br H Br H C C Br + Br Br -> Br C C Br + H Br
16 Br Br Br Br 1,1,1,2,2-pentabromoethane H Br Br Br Br C C Br + Br Br -> Br C C Br + H Br Br Br Br Br 1,1,1,2,2,2-hexabromoethane Uses of alkanes 1.Most alkanes are used as fuel e.g. Methane is used as biogas in homes.Butane is used as the Laboratory gas. 2.On cracking ,alkanes are a major source of Hydrogen for the manufacture of ammonia/Haber process. 3.In manufacture of Carbon black which is a component in printers ink. 4.In manufacture of useful industrial chemicals like methanol, methanol, and chloromethane. (ii) Alkenes (a)Nomenclature/Naming These are hydrocarbons with a general formula CnH2n and C C double bond as the functional group . n is the number of Carbon atoms in the molecule. The carbon atoms are linked by at least one double bond to each other and single bonds to hydrogen atoms.
(ii) Alkenes (a)Nomenclature/Naming These are hydrocarbons with a general formula CnH2n and C C double bond as the functional group . n is the number of Carbon atoms in the molecule. The carbon atoms are linked by at least one double bond to each other and single bonds to hydrogen atoms. They include: n General/ Molecular formula Structural formula Name 1 Does not exist 2 C2H6 H H H C C H Ethene
17 CH2 CH2 3 C3H8 H H H H C C C H H CH2 CH CH3 Propene 4 C4H10 H H H H H C C C C H H H CH2 CH CH2CH3 Butene 5 C5H12 H H H H H H C C C C C H H H H CH2 CH (CH2)2CH3 Pentene 6 C6H14 H H H H H H H C C C C C C H H H H H CH2 CH (CH2)3CH3 Hexene 7 C7H16 H H H H H H H H C C C C C C C H H H H H H H H Heptene
18 CH2 CH (CH2)4CH3 8 C8H18 H H H H H H H H H C C C C C C C C H H H H H H H CH2 CH (CH2)5CH3 Octene 9 C9H20 H H H H H H H H H H C C C C C C C C C H H H H H H H H CH2 CH (CH2)6CH3 Nonene 10 C10H22 H H H H H H H H H H H C C C C C C C C C C H H H H H H H H H CH2 CH (CH2)7CH3 decene Note 1.Since carbon is tetravalent ,each atom of carbon in the alkene MUST always be bonded using four covalent bond /four shared pairs of electrons including at the double bond. 2.Since Hydrogen is monovalent ,each atom of hydrogen in the alkene MUST always be bonded using one covalent bond/one shared pair of electrons. 3.One member of the alkene ,like alkanes,differ from the next/previous by a CH2 group.They also form a homologous series.
They include: n General/ Molecular formula Structural formula Name 1 Does not exist 2 C2H6 H H H C C H Ethene
17 CH2 CH2 3 C3H8 H H H H C C C H H CH2 CH CH3 Propene 4 C4H10 H H H H H C C C C H H H CH2 CH CH2CH3 Butene 5 C5H12 H H H H H H C C C C C H H H H CH2 CH (CH2)2CH3 Pentene 6 C6H14 H H H H H H H C C C C C C H H H H H CH2 CH (CH2)3CH3 Hexene 7 C7H16 H H H H H H H H C C C C C C C H H H H H H H H Heptene
18 CH2 CH (CH2)4CH3 8 C8H18 H H H H H H H H H C C C C C C C C H H H H H H H CH2 CH (CH2)5CH3 Octene 9 C9H20 H H H H H H H H H H C C C C C C C C C H H H H H H H H CH2 CH (CH2)6CH3 Nonene 10 C10H22 H H H H H H H H H H H C C C C C C C C C C H H H H H H H H H CH2 CH (CH2)7CH3 decene Note 1.Since carbon is tetravalent ,each atom of carbon in the alkene MUST always be bonded using four covalent bond /four shared pairs of electrons including at the double bond. 2.Since Hydrogen is monovalent ,each atom of hydrogen in the alkene MUST always be bonded using one covalent bond/one shared pair of electrons. 3.One member of the alkene ,like alkanes,differ from the next/previous by a CH2 group.They also form a homologous series. e.g Propene differ from ethene by one carbon and two Hydrogen atoms from ethene.
2.Since Hydrogen is monovalent ,each atom of hydrogen in the alkene MUST always be bonded using one covalent bond/one shared pair of electrons. 3.One member of the alkene ,like alkanes,differ from the next/previous by a CH2 group.They also form a homologous series. e.g Propene differ from ethene by one carbon and two Hydrogen atoms from ethene. 4.A homologous series of alkenes like that of alkanes: (i) differ by a CH2 group from the next /previous consecutively (ii)have similar chemical properties
19 (iii)have similar chemical formula represented by the general formula CnH2n (iv)the physical properties also show steady gradual change 5.The = C= C = double bond in alkene is the functional group. A functional group is the reacting site of a molecule/compound. 6. The = C= C = double bond in alkene can easily be broken to accommodate more two more monovalent atoms. The = C= C = double bond in alkenes make it thus unsaturated. 7. An unsaturated hydrocarbon is one with a double =C=C= or triple – C C – carbon bonds in their molecular structure. Unsaturated hydrocarbon easily reacts to be saturated. 8.A saturated hydrocarbon is one without a double =C=C= or triple – C C – carbon bonds in their molecular structure. Most of the reactions of alkenes take place at the = C = C =bond. (b)Isomers of alkenes Isomers are alkenes lie alkanes have the same molecular general formula but different molecular structural formula. Ethene and propene do not form isomers. Isomers of alkenes are also named by using the IUPAC(International Union of Pure and Applied Chemistry) system of nomenclature/naming. The IUPAC system of nomenclature of naming alkenes uses the following basic rules/guidelines: 1.Identify the longest continuous/straight carbon chain which contains the =C = C= double bond get/determine the parent alkene. 2.Number the longest chain form the end of the chain which contains the =C = C= double bond so he =C = C= double bond lowest number possible. 3 Indicate the positions by splitting “alk-positions-ene” e.g. but-2-ene, pent-1,3diene.
2.Number the longest chain form the end of the chain which contains the =C = C= double bond so he =C = C= double bond lowest number possible. 3 Indicate the positions by splitting “alk-positions-ene” e.g. but-2-ene, pent-1,3diene. 4.The position indicated must be for the carbon atom at the lower position in the =C = C= double bond.i.e But-2-ene means the double =C = C= is between Carbon “2”and “3” Pent-1,3-diene means there are two double bond one between carbon “1” and “2”and another between carbon “3” and “4” 5. Determine the position, number and type of branches. Name them as methyl, ethyl, propyl e.tc. according to the number of alkyl carbon chains attached to the alkene. Name them fluoro-,chloro-,bromo-,iodo- if they are halogens 6.Use prefix di-,tri-,tetra-,penta-,hexa- to show the number of double C = C bonds and branches attached to the alkene. 20 7.Position isomers can be formed when the=C = C= double bond is shifted between carbon atoms e.g. But-2-ene means the double =C = C= is between Carbon “2”and “3” But-1-ene means the double =C = C= is between Carbon “1”and “2” Both But-1-ene and But-2-ene are position isomers of Butene 8.Position isomers are molecules/compounds having the same general formular but different position of the functional group.i.e. Butene has the molecular/general formular C4H8 position but can form both But-1ene and But-2-ene as position isomers. 9. Like alkanes ,an alkyl group can be attached to the alkene. Chain/branch isomers are thus formed. 10.Chain/branch isomers are molecules/compounds having the same general formula but different structural formula e.g Butene and 2-methyl propene both have the same general formualr but different branching chain.
Like alkanes ,an alkyl group can be attached to the alkene. Chain/branch isomers are thus formed. 10.Chain/branch isomers are molecules/compounds having the same general formula but different structural formula e.g Butene and 2-methyl propene both have the same general formualr but different branching chain. Practice on IUPAC nomenclature of alkenes Name the following isomers of alkene H H H H H C C C C H But-1-ene H H H H H H H C C C C H But-2-ene H H H H H H H H H C C C C C C H 4-methylhex-1-ene H H H H C H
21 H H H C H H H H H H H C C C C C C H 4,4-dimethylhex-1-ene H H H H C H H 3. H H C H H H H H H C C C C C H 4,4-dimethylpent -1- ene H H H C H H 4. H H C H H H H H H C C C C C H 5,5-dimethylhex-2- ene H C H H H H C H H H
22 5. H H C H H H H H C C C C H 2,2-dimethylbut -2- ene H H H C H H 8.H2C CHCH2 CH2 CH3 pent -1- ene 9.H2C C(CH3)CH2 CH2 CH3 2-methylpent -1- ene 10.H2C C(CH3)C(CH3)2 CH2 CH3 2,3,3-trimethylpent -1- ene 11.H2C C(CH3)C(CH3)2 C(CH3)2 CH3 2,3,3,4,4-pentamethylpent -1- ene 12.H3C C(CH3)C(CH3) C(CH3)2 CH3 2,3,4,4-tetramethylpent -2- ene 13. H2C C(CH3)C(CH3) C(CH3) CH3 2,3,4-trimethylpent -1,3- diene 14.
I2C CICI CI2 1,1,2,3,4,4-hexaiodobut -1,3- diene 18. H2C C(CH3)C(CH3) CH2 2,3-dimethylbut -1,3- diene (c)Occurrence and extraction
23 At indusrial level,alkenes are obtained from the cracking of alkanes.Cracking is the process of breaking long chain alkanes to smaller/shorter alkanes, an alkene and hydrogen gas at high temperatures. Cracking is a major source of useful hydrogen gas for manufacture of ammonia/nitric(V)acid/HCl i.e. Long chain alkane -> smaller/shorter alkane + Alkene + Hydrogen gas Examples 1.When irradiated with high energy radiation,Propane undergo cracking to form methane gas, ethene and hydrogen gas. Chemical equation CH3CH2CH3 (g) -> CH4(g) + CH2=CH2(g) + H2(g) 2.Octane undergo cracking to form hydrogen gas, butene and butane gases Chemical equation CH3(CH2) 6 CH3 (g) -> CH3CH2CH2CH3(g) + CH3 CH2CH=CH2(g) + H2(g) (d)School laboratory preparation of alkenes In a school laboratory, alkenes may be prepared from dehydration of alkanols using: (i) concentrated sulphuric(VI)acid(H2SO4). (a) aluminium(III)oxide(Al2O3) i.e Alkanol --Conc. H2SO4 --> Alkene + Water Alkanol --Al2O3 --> Alkene + Water e.g. 1.(a)At about 180oC,concentrated sulphuric(VI)acid dehydrates/removes water from ethanol to form ethene. The gas produced contain traces of carbon(IV)oxide and sulphur(IV)oxide gas as impurities. It is thus passed through concentrated sodium/potassium hydroxide solution to remove the impurities.
1.(a)At about 180oC,concentrated sulphuric(VI)acid dehydrates/removes water from ethanol to form ethene. The gas produced contain traces of carbon(IV)oxide and sulphur(IV)oxide gas as impurities. It is thus passed through concentrated sodium/potassium hydroxide solution to remove the impurities. Chemical equation CH3CH2OH (l) --conc H2SO4/180oC--> CH2=CH2(g) + H2O(l) (b)On heating strongly aluminium(III)oxide(Al2O3),it dehydrates/removes water from ethanol to form ethene. 24 Ethanol vapour passes through the hot aluminium (III) oxide which catalyses the dehydration. Activated aluminium(III)oxide has a very high affinity for water molecules/elements of water and thus dehydrates/ removes water from ethanol to form ethene. Chemical equation CH3CH2OH (l) --(Al2O3/strong heat--> CH2=CH2(g) + H2O(l) 2(a) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by conc H2SO4 at about 180oC to propene(propene has no position isomers).
24 Ethanol vapour passes through the hot aluminium (III) oxide which catalyses the dehydration. Activated aluminium(III)oxide has a very high affinity for water molecules/elements of water and thus dehydrates/ removes water from ethanol to form ethene. Chemical equation CH3CH2OH (l) --(Al2O3/strong heat--> CH2=CH2(g) + H2O(l) 2(a) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by conc H2SO4 at about 180oC to propene(propene has no position isomers). Chemical equation CH3CH2 CH2OH (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene (b) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by heating strongly aluminium(III)oxide(Al2O3) form propene Chemical equation CH3CH2 CH2OH (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene 3(a) Butan-1-ol and Butan-2-ol(position isomers of butanol) are dehydrated by conc H2SO4 at about 180oC to But-1-ene and But-2-ene respectively Chemical equation CH3CH2 CH2 CH2OH (l) -- conc H2SO4/180oC -->CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene CH3CHOH CH2CH3 (l)-- conc H2SO4/180oC -->CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene (b) Butan-1-ol and Butan-2-ol are dehydrated by heating strongly aluminium (III) oxide (Al2O3) form But-1-ene and But-2-ene respectively.
Activated aluminium(III)oxide has a very high affinity for water molecules/elements of water and thus dehydrates/ removes water from ethanol to form ethene. Chemical equation CH3CH2OH (l) --(Al2O3/strong heat--> CH2=CH2(g) + H2O(l) 2(a) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by conc H2SO4 at about 180oC to propene(propene has no position isomers). Chemical equation CH3CH2 CH2OH (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene (b) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by heating strongly aluminium(III)oxide(Al2O3) form propene Chemical equation CH3CH2 CH2OH (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene 3(a) Butan-1-ol and Butan-2-ol(position isomers of butanol) are dehydrated by conc H2SO4 at about 180oC to But-1-ene and But-2-ene respectively Chemical equation CH3CH2 CH2 CH2OH (l) -- conc H2SO4/180oC -->CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene CH3CHOH CH2CH3 (l)-- conc H2SO4/180oC -->CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene (b) Butan-1-ol and Butan-2-ol are dehydrated by heating strongly aluminium (III) oxide (Al2O3) form But-1-ene and But-2-ene respectively. Chemical equation CH3CH2 CH2 CH2OH (l) -- Heat/Al2O3 --> CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene
25 CH3CHOH CH2CH3 (l) -- Heat/Al2O3 --> CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene Laboratory set up for the preparation of alkenes/ethene Caution (i)Ethanol is highly inflammable (ii)Conc H2SO4 is highly corrosive on skin contact.
Chemical equation CH3CH2OH (l) --(Al2O3/strong heat--> CH2=CH2(g) + H2O(l) 2(a) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by conc H2SO4 at about 180oC to propene(propene has no position isomers). Chemical equation CH3CH2 CH2OH (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene (b) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by heating strongly aluminium(III)oxide(Al2O3) form propene Chemical equation CH3CH2 CH2OH (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene 3(a) Butan-1-ol and Butan-2-ol(position isomers of butanol) are dehydrated by conc H2SO4 at about 180oC to But-1-ene and But-2-ene respectively Chemical equation CH3CH2 CH2 CH2OH (l) -- conc H2SO4/180oC -->CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene CH3CHOH CH2CH3 (l)-- conc H2SO4/180oC -->CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene (b) Butan-1-ol and Butan-2-ol are dehydrated by heating strongly aluminium (III) oxide (Al2O3) form But-1-ene and But-2-ene respectively. Chemical equation CH3CH2 CH2 CH2OH (l) -- Heat/Al2O3 --> CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene
25 CH3CHOH CH2CH3 (l) -- Heat/Al2O3 --> CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene Laboratory set up for the preparation of alkenes/ethene Caution (i)Ethanol is highly inflammable (ii)Conc H2SO4 is highly corrosive on skin contact. (iii)Common school thermometer has maximum calibration of 110oC and thus cannot be used.
Chemical equation CH3CH2 CH2OH (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- conc H2SO4/180oC --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene (b) Propan-1-ol and Propan-2-ol(position isomers of propanol) are dehydrated by heating strongly aluminium(III)oxide(Al2O3) form propene Chemical equation CH3CH2 CH2OH (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-1-ol Prop-1-ene CH3CHOH CH3 (l) -- Heat/Al2O3 --> CH3CH2=CH2(g) + H2O(l) Propan-2-ol Prop-1-ene 3(a) Butan-1-ol and Butan-2-ol(position isomers of butanol) are dehydrated by conc H2SO4 at about 180oC to But-1-ene and But-2-ene respectively Chemical equation CH3CH2 CH2 CH2OH (l) -- conc H2SO4/180oC -->CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene CH3CHOH CH2CH3 (l)-- conc H2SO4/180oC -->CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene (b) Butan-1-ol and Butan-2-ol are dehydrated by heating strongly aluminium (III) oxide (Al2O3) form But-1-ene and But-2-ene respectively. Chemical equation CH3CH2 CH2 CH2OH (l) -- Heat/Al2O3 --> CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene
25 CH3CHOH CH2CH3 (l) -- Heat/Al2O3 --> CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene Laboratory set up for the preparation of alkenes/ethene Caution (i)Ethanol is highly inflammable (ii)Conc H2SO4 is highly corrosive on skin contact. (iii)Common school thermometer has maximum calibration of 110oC and thus cannot be used. It breaks/cracks.
Chemical equation CH3CH2 CH2 CH2OH (l) -- Heat/Al2O3 --> CH3 CH2CH2=CH2(g) + H2O(l) Butan-1-ol But-1-ene
25 CH3CHOH CH2CH3 (l) -- Heat/Al2O3 --> CH3CH=CH CH2(g) + H2O(l) Butan-2-ol But-2-ene Laboratory set up for the preparation of alkenes/ethene Caution (i)Ethanol is highly inflammable (ii)Conc H2SO4 is highly corrosive on skin contact. (iii)Common school thermometer has maximum calibration of 110oC and thus cannot be used. It breaks/cracks. (i)Using conentrated sulphuric(VI)acid Some broken porcelain or sand should be put in the flask when heating to: (i)prevent bumping which may break the flask. (ii)ensure uniform and smooth boiling of the mixture The temperatures should be maintained at above160oC. At lower temperatures another compound -ether is predominantly formed instead of ethene gas. (ii)Using aluminium(III)oxide
26 (e)Properties of alkenes I. Physical properties Like alkanes, alkenes are colourles gases, solids and liquids that are not poisonous. They are slightly soluble in water. The solubility in water decrease as the carbon chain and as the molar mass increase but very soluble in organic solvents like tetrachloromethane and methylbenzene. The melting and boiling point increase as the carbon chain increase. This is because of the increase in van-der-waals /intermolecular forces as the carbon chain increase. The 1st four straight chain alkenes (ethene,propane,but-1-ene and pent-1-ene)are gases at room temperature and pressure. The density of straight chain alkenes,like alkanes, increase with increasing carbon chain as the intermolecular forces increases reducing the volume occupied by a given mass of the alkene.