S4 Chemistry National 5

Transcription

1 S4 hemistry National 5 Nature s hemistry Unit ourse Notes- ydrocarbons and onsumer Products Name lass 1

2 ydrocarbons ydrocarbons can be categorised into family groups known as OMOLOGOUS SERIES. A homologous series is a group of hydrocarbons with the SAME GENERAL FORMULA and similar properties. Alkanes The first homologous series is known as the Alkanes. they contain only single (saturated) bonds have the general formula n 2n+2. burn to produce carbon dioxide and water boiling points, melting points and viscosity increases with increasing number of carbon atoms. insoluble in water Alkanes can be identified by the ane ending and a prefix which indicates the number of carbon atoms in the molecules. Prefix Number of atoms Prefix Number of atoms meth 1 pent 5 eth 2 hex 6 prop 3 hept 7 but 4 oct 8 The names, molecular formulae, shortened and full structural formulae for the first eight alkanes are shown below. Name Molecular Formula Shortened Structural Formula methane 4 4 ethane propane butane pentane hexane heptane

3 octane Name Full Structural Formula Name Full Structural Formula methane pentane ethane hexane propane heptane butane octane 3

4 Alkenes The second homologous series of hydrocarbons are the alkenes. they contain at least one carbon to carbon double bond = (unsaturated bond). have the general formula n2n burn to produce carbon dioxide and water boiling points,melting points and viscosity increases with increasing number of carbon atoms. insoluble in water are much more reactive than alkanes used to make polymers and alcohols Note: a feature such as the = bond which identifies a hydrocarbon as belonging to a family is called a functional group. Uses of Alkenes Small alkenes such as ethene and propene are used in the plastics industry to make polythene and polypropene. You will find out more about these in unit 3. Alkenes can be identified by the ene ending to their names. The names, molecular formulae, shortened and full structural formulae for the first seven alkenes are shown below. Name Molecular Formula Shortened Structural Formula ethene = 2 propene = 3 butene = 2 3 4

5 pentene = hexene = heptene = octene = Name Full Structural Formula Name Full Structural Formula ethene = hexene = propene = heptene = butene = octene = Pentene = ycloalkanes Nat 5 The third homologous series of hydrocarbons are the cycloalkanes they have a ring structure and contain only single bonds have the general formula n2n burn to produce carbon dioxide and water boiling points increase with increasing number of carbon. insoluble in water. used as fuels and solvents 5

6 ycloalkanes can be identified by the ane ending and a prefix which starts with cyclo and indicates the number of carbon atoms in the molecules. The names, molecular formulae, shortened and full structural formulae for the first four cycloalkanes are shown below. Name Molecular Formula cyclopropane 3 6 cyclobutane 4 8 cyclopentane 5 10 cyclohexane 6 12 cycloheptane 7 14 cyclooctane 8 16 Name Full Structural Formula Name Full Structural Formula cyclopropane cyclohexane cyclobutane cycloheptane cyclopentane cyclooctane 6

7 Uses of ycloalkanes yclopentane is used in place of Fs in refrigerators, cyclohexane in the manufacture of nylon and cycloheptane is used as an industrial solvent. Saturated and Unsaturated Saturated hydrocarbons contain only single bonds (the carbons are are full up with hydrogens). The alkanes and cycloalkanes are examples of saturated hydrocarbons. Unsaturated hydrocarbons contain at least one carbon to carbon double bond. The alkenes are examples of unsaturated hydrocarbons. Reactions of Alkenes Alkenes, because they are unsaturated, are more reactive than alkanes and cycloalkanes. The double bond allows them to undergo addition reactions with halogens, hydrogen and water. ydrogenation Alkenes undergo addition reactions with hydrogen to form the corresponding alkane. In the reaction the double bond breaks open and the two hydrogen atoms add on to the carbons on either side. = = Ethene + ydrogen Ethane (unsaturated) (saturated) 7

8 Adding hydrogen across a double bond changes the unsaturated alkene into the saturated alkane. ydration Alkenes undergo addition reactions with water to form the corresponding alcohol. In the reaction the double bond breaks open and the hydrogen adds to one carbon while the hydroxide adds to the other carbon. O = + - O 2 = O 3 2 O Ethene + Water Ethanol (unsaturated) (alcohol) Adding water across a double bond changes the unsaturated alkene into the alcohol. alogenation Alkenes undergo addition reactions with halogens to form the corresponding dihaloalkanes. In the reaction the double bond breaks open and the two halogen atoms add on to the carbons on either side. Br Br = + Br - Br 8

9 2 = 2 + Br 2 2 Br 2 Br Ethene + Bromine Dibromoethane (unsaturated) (dihaloalkane) Adding a halogen across a double bond changes the unsaturated alkene into the dihaloalkane. Identifying an Alkene An unsaturated hydrocarbon can be distinguished from a saturated hydrocarbon by testing with bromine solution. When bromine, which is brown, is added to an alkene (unsaturated) it is instantly decolourised because the bromine adds the double bond. This does not happen with an alkane or cycloalkane. Br Br = + Br - Br Br Br 2 (colourless) (Brown) (colourless) Alkanes and cycloalkanes do not undergo addition reactions. 9

10 Isomers Isomers are molecules with the same molecular formulae but different structural formulae. Alkanes can have isomers with branched chains. Two examples of 4 10 can be: Alkenes can have isomers with branched chains and also with the double bond in a different position. Two examples of 4 8 can be: = = ycloalkanes are isomers of the corresponding alkenes. Two examples of 3 6 can be: = Propene ( 3 6 ) yclopropane ( 3 6 ) Isomers have different properties from each other. e.g. Propene will decolourise bromine solution. yclopropene will not decolourise bromine solution. 10

11 Naming Branched Alkanes To name a branched alkane Select the longest continuous chain of carbon atoms and name it after the appropriate straight chain alkane. Number the carbon atoms from the end of the chain nearer the branch. Name the branch(es) and indicate the position(s) of the branch(es) on the chain. Number of Name of branch carbons in branch 1 methyl 2 ethyl 3 propyl 4 butyl 1 Main chain = butane 2 Branch = methyl 3 Position = 2 4 The complete name is 2-methylbutane 1 Main chain = pentane 2 Branch = ethyl 3 Position = 3 4 The complete name is 3-ethylpentane 11

12 Naming Branched Alkanes continued 1 Main chain = butane 2 Branch = methyl 3 Position = 2,2 4 The complete name is 2,2-dimethylbutane di is used as there are two methyl groups 12

13 Naming Branched Alkenes To name a branched alkene Select the longest continuous chain of carbon atoms containing the double bond and name it after the appropriate straight chain alkene. Number the carbon atoms from the end of the chain nearer the double bond and indicate the position of the double bond. Name any branch(es) and indicate the position(s) of the branch(es) on the chain. 1 Main chain = butene 2 Double bond position = 1 3 Branch position = 3 4 Branch = methyl 5 The complete name is 3 methylbut-1-ene 13

14 onsumer Products Alcohols Alcohols are a family of compounds that contain the characteristic ydroxyl (O) functional group. Their names end with the letters ol. Straight and branched chain alcohols are identified and named from the structural formulae. The systematic name of alcohols details the position of the O functional group. e.g. O O Butan-1-ol Butan-2-ol Given the name of any alcohol the structural and molecular formulae of the compounds can be deduced. As alcohols increase in size their melting and boiling points increase. This is due to the increasing strength of the intermolecular forces i.e. the attractions between the molecules. Alcohols are miscible with water. owever, the solubility decreases as size increases from butanol onwards. Alcohols make good fuels as they are highly flammable and burn with clean flames. They are also used as solvents. 14

15 arboxylic Acids arboxylic Acids are a family of compounds that contain the characteristic arboxyl (OO) functional group. Their names end with the letters oic acid The OO functional group is found at the end of the main carbon chain. Straight and branched chain arboxylic Acids are identified and named from the structural formulae. e.g. O O Butanoic acid Given the name of any arboxylic Acid the structural and molecular formulae of the compounds can be deduced. As carboxylic acids increase in size their melting and boiling points increase due to the increasing strength of the intermolecular forces. arboxylic acids are miscible with water. owever, the solubility decreases as size increases from pentanoic acid onwards. In general, carboxylic acids are used in the preparation of preservatives, soaps and medicines. Vinegar is a solution of Ethanoic Acid. Vinegar can be used in household cleaning products as it is non-toxic. 15

16 arboxylic acids, just like other acids, have a p less than 7 when in solution. They can be used to neutralise alkaline solutions and will react with metal oxides, hydroxides and carbonates to form salts. The salt can be named from the metal in the base and the acid used in the reaction. e.g. sodium hydroxide + ethanoic acid sodium ethanoate potassium hydroxide + propanoic acid potassium propanoate Energy from Fuels Exothermic reactions are reactions which give out heat energy to their surroundings such as the combustion of alkanes and alcohols. The reverse of this reaction is known as an endothermic reaction where heat energy is absorbed from the surroundings. We burn fuels to release the stored chemical energy within them, also known as combustion. ombustion is an exothermic reaction. For combustion to take place, oxygen must be present. The products of combustion are water and carbon dioxide. owever, if there is not a plentiful supply of oxygen, carbon monoxide, carbon (soot) and water are produced. This is known as incomplete combustion. General word equation (combustion): Fuel + oxygen -> carbon dioxide + water Example chemical equation: 4 (g) + 2O 2 (g) -> O 2 (g) O(l) 16

17 It is possible to calculate the energy released from a fuel by taking some simple measurements and using the calculation E h = cm T E h = enthalpy of combustion (in kj) c = specific eat apacity of water (is always 4.18 kj kg -1 o -1 ), m = mass of heated water (in kg must divide cm3 by 1000), T = change in water temp ( o ) Experimental Method 1. Set up the apparatus above. 2. Record the starting temperature of the water, then heat the water with your chosen fuel for 30 seconds. 3. Record the end temperature and calculate the change in temperature. 17

18 4. Repeat steps 2 and 3 twice. You can then use your results to calculate the energy released using E h = cm T Example alculations: Example 1 alculate the energy released, in kj, when propanol heats 50cm3 of water by 13o E h = cm T = 4.18 x 0.05 x 13 = 2.7kJ Example 2 alculate the energy released, in kj, when ethanol heats 200cm3 of water from 22o to 29o E h = cm T = 4.18 x 0.2 x 7 = 5.9kJ 18

19 ydrocarbons What you Should Know overed ( ) ow well can you do this? 1. ydrocarbons contain only hydrogen and carbon 2. Alkanes are a family of hydrocarbons 3. Alkanes are saturated and contain only single - bonds 4. Alkanes have the general formula n 2n+2 5. Uses of alkanes include fuels, lubricating oil, and tar. 6. Alkenes are a family of unsaturated hydrocarbons and contain a = double bond and begin with ethene 7. Alkenes are produced by cracking. 8. Alkenes are used to make plastics 9. Alkenes general formula is n 2n 10. The boiling point, melting point and viscosity(thickness) of alkanes and alkenes increases with size 11. Draw structural formulae for alkanes and alkenes up to 8 carbons 12. ycloalkanes are a family of hydrocarbons with a ring structure 13. ycloalkanes begin with cyclopropane 14. ycloalkanes have the general formula n 2n 15. Give uses for cycloalkanes 16. Draw structural formula up to cycloalkanes with 8 carbons 17. Alkanes and alkenes can have branches 18. Systematic naming is used to identify branched alkanes and alkenes 19

20 19. Alkenes can take part in addition reactions forming alkanes and alcohols 20. Isomers have the same molecular formula but a different structural formula 21. Isomers have different properties. 20

21 onsumer Products - What you Should Know overed ( ) ow well can you do this? 23. Alcohols contain the O, hydroxyl group 24. Position of O given in systematic name. 25. Name and draw alcohols Alcohols are good fuels as the burn cleanly and are highly flammable 27. Alcohols are used as solvents and fuels 28. Methanol, ethanol and propanol are miscible with water, thereafter the solubility decreases as size increases. 29. As alcohols increase in size their melting and boiling points increase due to the increasing strength of the intermolecular forces. 30. arboxylic acids contain the OO group 31. The OO group always comes at the end of the chain 32. Draw and name carboxylic acid from Methanoic, ethanoic, propanoic and butanoic acid are miscible in water, thereafter the solubility decreases as size increases. 34. As carboxylic acids increase in size their melting and boiling points increase due to the increasing strength of the intermolecular forces. 35. arboxylic acids are used in the preparation of preservatives, soaps and medicines. 21

22 36. Solutions of carboxylic acids have a p less than 7 and can react with metals, metal oxides, hydroxides and carbonates forming salts. 37. Salts formed from straight-chain carboxylic acids containing no more than 8 carbons, can be named. 38. A reaction or process that releases heat energy is described as exothermic. A reaction or process that takes in heat energy is described as endothermic. 39. In combustion, a substance reacts with oxygen releasing energy. 40. ydrocarbons and alcohols burn in a plentiful supply of oxygen to produce carbon dioxide and water. Equations can be written for the complete combustion of hydrocarbons and alcohols. 41. Fuels burn releasing different quantities of energy. 42. The quantity of heat energy released can be determined experimentally and calculated using, E h = cmδt. 43. The quantities E h, c, m or ΔT can be calculated, in the correct units, given relevant data. alculations can involve heating substances other than water. 22