New Town Secondary School Alkanes and Alkenes_2023

Page 1 New Town Secondary School Secondary 4E Pure Chemistry Name: ( ) Class: Date: Organic Chemistry – Alkanes and Alkenes Syllabus At the end of this topic, students should be able to: 11.2b Describe the alkanes as a homologous series of saturated hydrocarbons with the general formula CnH2n+2. 11.2c Draw the structures of branched and unbranched alkanes, C1 to C4, and name the unbranched alkanes methane to butane. 11.2d Define isomerism and identify isomers. 11.2e Describe the properties of alkanes (exemplified by methane) as being generally unreactive except in terms of combustion and substitution by chlorine. 11.3a Describe the alkenes as a homologous series of unsaturated hydrocarbons with the general formula CnH2n. 11.3b Draw the structures of branched and unbranched alkenes, C2 to C4, and name the unbranched alkenes ethene to butene. 11.3c Describe the manufacture of alkenes and hydrogen by cracking hydrocarbons and recognise that cracking is essential to match the demand for fractions containing smaller molecules from the refinery process. 11.3d Describe the difference between saturated and unsaturated hydrocarbons from their molecular structures and by using aqueous bromine. 11.3e Describe the properties of alkenes (exemplified by ethene) in terms of combustion, polymerisation and the addition reactions with bromine, steam and hydrogen. 11.3f State the meaning of polyunsaturated when applied to food products. 11.3g Describe the manufacture of margarine by the addition of hydrogen to unsaturated vegetable oils to form a solid product.

Page 2 Alkanes Alkanes are saturated hydrocarbons with the general formula of CnH2n+2. This means that each alkane molecule contains only carbon and hydrogen atoms, and each carbon aom is covalently bonded to four other atoms. As with all homologous series, the physical properties of individual members changes with increasing mass/length of carbon chain. Name Formula Melting Point (°C) Boiling Point (°C) State at r.t.p. Density (g/cm3) Flammable Methane CH4 – 182 – 162 Gas 0.424 Most Ethane C2H6 – 183 – 89 Gas 0.546 Propane C3H8 – 188 – 42 Gas 0.584 Butane C4H10 – 138 0 Gas 0.601 Pentane C5H12 – 130 36 Liquid 0.626 Hexane C6H14 – 95 69 Liquid 0.659 Heptane C7H16 – 91 98 Liquid 0.684 Octane C8H18 – 57 126 Liquid 0.703 Nonane C9H20 – 54 151 Liquid 0.718 Decane C10H22 – 30 174 Liquid 0.730 Least Isomerism In organic chemistry, molecules with the same molecular formula but different structural formula are known as structural isomers. Types of structural isomers • Organic molecules with the same molecular formula but differ in their structure with respect to the position of the functional group. (Positional isomers) • Organic molecules with the same molecular formula but differ in their structure with respect to the length of the longest carbon chain. (Chain Isomers) Positional Isomers Propanol (C3H7OH) Propan-1-ol Propan-2-ol Propan-1-ol Number of posit