Organic chemistry combined chem notes

Chapter 15: Fuels and Crude Oil 15.1 - Importance of natural gas and crude oil in our lives Methane and crude oil are non-renewable sources of energy 15.2 - Separation of crude oil/petroleum Crude oil Crude oil contains a mixture of hydrocarbons Hydrocarbons are compounds containing carbon and hydrogen only Separation of crude oil Name (in order of fractions) No. of carbon atoms Boiling point/ °C Uses Liquefied petroleum gas (LPG) 1-4 40< Fuel for cooking Petrol (gasoline) 5-10 40-75 Fuel in cars Naphtha 7-14 75-150 Feedstock for the petrochemical industry Kerosene (paraffin) 11-16 160-250 Fuel for heating and cooking Fuel for aircraft engines Diesel 16-20 250-300 Fuel for diesel engine Lubricating oils 20-50 300-350 Lubricants For polishes and waxes Bitumen >50 >350 Making road surfaces Mnemonic Love Pushing Naughty Kids Down Oversized Bags Process of separation Fractional distillation: - Crude oil is heated and turns into vapour, then enters the fractionating column - As hot vapour rises up the column, it cools and condenses at different temperatures - The fractions with the lowest boiling point condense at the top , then removed - The fractions with the highest boiling points condense at the bottom

15.3 - Changes in properties for different fractions As the size and mass of the hydrocarbons increase down the fractions from LPG to Bitumen : Boiling point increase When the size of molecules increases, intermolecular forces of attraction increase, and more energy is needed to overcome these forces Viscosity increase When the size of molecules increases, intermolecular forces of attraction increase, the forces are harder to overcome, and the larger hydrocarbons do not flow easily Flammability decreases When the size of the hydrocarbon increases, the percentage of mass of hydrogen in the molecule decreases, and hydrogen is flammable Competing uses of crude oil - It is non-renewable - To meet the competing uses of crude oil, there is a growing need for its conservation - Thus, use alternatives like solar energy, biofuels Biofuels Bioethanol is obtained by fermentation of sugar in sugarcane to ethanol (seen in 17.1) Ethanol + Oxygen → CO 2 + Water Better for the environment because it offsets the carbon dioxide emission during burning by absorbing carbon dioxide during plant growth Chapter 16/17: Alkanes and Alkenes, Alcohols and Carboxylic Acids 16.1 - Organic chemistry Organic compounds are a class of chemical compounds in which one or more atoms are covalently bonded to atoms of other elements Homologous series - A general formula - Similar chemical properties due to the same functional group - A gradual change in physical properties as a result of the increase in size/mass of the molecules - Successive members differ by – CH ₂

A functional group is a combination of atoms which gives organic compounds their distinctive properties As the size and mass of the organic molecule increase: - Melting and boiling point increases - Viscosity increase - Flammability decrease Prefixes and suffixes Prefix No. of carbon atoms Suffix Homologous series Meth- 1 -ane Alkane Eth- 2 -ene Alkene Pro- 3 -anol Alcohol But- 4 -anoic acid Carboxylic acid 16.2 - Alkanes Alkanes - A homologous series - Functional group: Has saturated hydrocarbons (carbon-carbon single bonds only) - General formula: C n H 2n+2 Physical Properties - Gas at RTP Chemical properties Alkanes are generally unreactive Alkane undergo 2 reactions - Combustion - Substitution by chlorine

Combustion - Complete combustion Alkanes burn in excess/sufficient air with a blue (non-luminous) flame The products are carbon dioxide and water Methane + oxygen → carbon dioxide + water CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O (g) - Incomplete combustion Alkanes burn in limited amount of air with a yellow smoky (luminous) flame Possible products are carbon (soot), carbon monoxide and water Methane + oxygen → carbon monoxide + water 2CH 4 (g) + 3O 2 (g) → 2CO(g) + 4H 2 O(g) Methane + oxygen → carbon + water CH 4 (g) + O 2 (g) → C(g) + 2H 2 O(g) Substitution by chlorine The reaction takes place in the presence of sunlight (UV light) as the catalyst. Each hydrogen in the alkane is replaced one at a time by one molecule of chlorine to form chloroalkanes Substitution is a random process where any hydrogen has an equal chance of being replaced by chlorine Example:

During a substitution reaction, the mixture will contain all the above substances – CH 4 , CH 3 Cl, CH 2 Cl 2 , CHCl 3 , CCl 4 , and Cl 2 , HCl at the same time Preparation Alkanes are obtained directly from the fractional distillation of crude oil 16.3 - Alkenes Alkenes - A homologous series - Functional group: Has unsaturated hydrocarbons (contain carbon-carbon double bonds) - General formula: C n H 2n Physical Properties - Gas at RTP Chemical properties In a carbon-carbon double bond, each carbon atom is only covalently bonded to 3 atoms Meaning a new atom can be added to it Thus, alkenes are reactive since they are unsaturated Alkenes undergo 3 reactions - Combustion - Hydrogenation - Bromination - Addition polymerisation

Combustion - Complete combustion Alkenes burn in excess oxygen Methane + oxygen → carbon dioxide + water C 2 H 4 (g) + 3O 2 (g) → 2CO 2 (g) + 2H 2 O(g) - Incomplete combustion Alkanes burn in limited amount of oxygen Possible products are carbon (soot), carbon monoxide and water ethene + oxygen → carbon monoxide + water 2C 2 H 4 (g) + 3O 2 (g) → 2CO(g) + 4H 2 O(g) Methane + oxygen → carbon + water CH 4 (g) + O 2 (g) → C(g) + 2H 2 O(g) Hydrogenation Alkene + Hydrogen → Alkane Conditions: 200°C, nickel catalyst Bromination Alkene + Bromine C 2 H 4 + Br 2 → C 2 H 4 Br 2 Test for unsaturated hydrocarbons Addition polymerisation Monomers react with one another to form long molecules called polymers Conditions: High temperature and pressure, catalyst Preparation of alkene through Cracking Large alkane → smaller alkane + alkene Or Large alkane → alkene + Hydrogen

Used to produce alkene, hydrogen, small alkane molecules which are essential to match the demand for fractions containing smaller molecules Conditions: High temperature (600°C), solid catalyst (aluminium oxide, silicon (IV) oxide) 16.4 - Fats and oils Polyunsaturated fats contain a lot of carbon-carbon double bonds Such as vegetable oil Hydrogenating polyunsaturated fats causes it to be solid, which is easier to store Vegetable oil + H 2 → Margarine 17.1 - Alcohols Not a hydrocarbon Alcohols - A homologous series - Functional group called hydroxyl, -O-H - General formula: C n H 2n+1 OH

Physical Properties - Soluble in water - Liquid at RTP As size and mass of alcohol molecule increase: - Solubility in water decreases Chemical properties Undergoes 2 reactions - Combustion - Oxidation of alcohol to