IGCSE Double Award Extended Coordinated Science - Organic Chemistry PDF

# IGCSE Double Award Extended Coordinated Science ## Topic C8 - Organic Chemistry ### Homologous Series You need to know the concept of homologous series. - A homologous series can be described as a 'family' of similar compounds with similar properties due to the same functional group and same gen...

# IGCSE Double Award Extended Coordinated Science ## Topic C8 - Organic Chemistry ### Homologous Series You need to know the concept of homologous series. - A homologous series can be described as a 'family' of similar compounds with similar properties due to the same functional group and same general formula - Same functional group means that they chemically react in a similar way - Same general formula means that they contain the same type/number of atoms, which gives them similar physical properties - As you go through a homologous series, they increase by a -CH2 each time (gives gradual change in the physical properties e.g. increase in C-chain length, increases boiling point). **Key homologous series:** - Alkanes - Alkenes - Alcohols - Carboxylic acids (Triple) - Esters (Triple) When naming a member of a homologous series, we first start with the number of carbons in the continuous carbon chain (and then the end of the name comes from the homologous series). You will only be asked to draw/name up to 4 carbons in length. - 1 carbon - meth- e.g. methane - 2 carbons - eth- e.g. ethane - 3 carbons - prop- e.g. propane - 4 carbons - but- e.g. butane ### Alkanes You need to know how to draw & name alkanes (up to 4 carbons long) and describe their properties and reactions. Alkanes are the simplest homologous series, containing only single covalent C-C/C-H bonds - they are said to be "saturated". They are also 'hydrocarbons' as they are molecules that only contain carbon and hydrogen atoms. - General info: - No special functional group (C-C) - '-ane' in their name - CnH2n+2 The C-C/C-H bonds are strong, making alkanes relatively unreactive with acids/alkalis, and they are generally immiscible with water (they do not mix). However, they can undergo combustion and be used as a fuel e.g. methane. **Fuel + oxygen → carbon dioxide + water** - **Complete combustion:** (plentiful supply of oxygen) - Methane + oxygen → carbon dioxide + water - CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) - **Incomplete combustion:** (limited supply of oxygen) - Methane + oxygen → carbon monoxide + water - CH4(g) + 1.5O2(g) → CO(g) + 2H2O(g) - Methane + oxygen → carbon (soot/particulates) + water - CH4(g) + O2(g) → C(g) + 2H2O(g) ### Condensation polymerisation Form when monomers with different functional groups join to form long chain molecules and small molecules of water are eliminated. - They can be natural (e.g. proteins) or synthetic. - There are two main types needed at IGCSE: - Polyamides - Polyesters (TRIPLE) **NYLON** - **Polyamide** - The linkage is called an amide/peptide - Water is lost before the monomers join - Two different functional groups - amine & carboxylic acid **The diagram above is the general process, but you need to draw the actual monomers given to you in the exam question** ### Cracking Cracking breaks long-chain hydrocarbons (alkanes) into shorter alkanes & alkenes (and sometimes hydrogen) as there is a greater demand for these (they are easier to ignite/more useful regents etc.). - Both products of this process are useful. **Various product combinations possible but:** - Number of atoms stays the same - Mix of smaller alkanes and alkenes formed (and sometimes hydrogen, H2) **Two types of cracking:** - Catalytic - Thermal - 1) THERMAL - High temperature ~750°C - High PRESSURE ~70atm - 2) CATALYTIC - LOW temperature/PRESSURE ~500°C - Use of a catalyst **ZEOLITE** ### Polymerisation You need to know the process of polymerisation via addition and condensation reactions. - **Two types:** - Addition (see alkenes section) - Condensation - Different polymers have different units (monomers) and/or different linkages that give them their individual properties. ### Fractional distillation & Cracking You need to know the products of fractional distillation and cracking and understand the general process. - Crude oil/petroleum is a mixture of hydrocarbons that can be separated into its useful parts (fractions) by the process of fractional distillation. Each fraction is still a mixture, but they are of similar size e.g. 3-8 carbons in length, and have different uses related to their properties. | Position leaving fractionating column | Name of product | Use (Pink = Triple) | |---|---|---| | 1 (top) | Refinery gas | Bottled gas for heating/cooking | | 2 | Gasoline | Fuel (petrol) in cars | | 3 | Naphtha | Making chemicals | | 4 | Kerosene/paraffin | Jet fuel | | 5 | Diesel oil/gas oil | Fuel in diesel engines | | 6 | Fuel oil | Fuel for ships and home heating systems | | 7 | Lubricating oil | Lubricants, waxes, polishes | | 8 (bottom) | Bitumen | Making road surfaces | **As you go UP the fractionating column:** - Carbon chain of the hydrocarbon gets shorter (so lower boiling point as less energy needed to overcome forces of attraction) - Compounds are more flammable - Viscosity (thickness) decreases - Lighter in colour - Volatility increases (due to lower boiling point) - Compounds collected at the very top of the column are gases. ### Fuels You need to know the names of some fossil fuels, and that they produce carbon dioxide on combustion. - Fuel = substance that reacts rapidly with oxygen to release a lot of energy. **Fossil fuels:** - Coal - Natural gas (mainly methane, CH4 from decomposition of organic matter) - Petroleum/crude oil **Fuel + oxygen → carbon dioxide + water** - **Fuels are a finite resource (will run out) and also release carbon dioxide during combustion, so chemists are searching for alternative fuels and feedstocks.** - "Gasohol" - mixing ethanol with gasoline - Developing fuel from fermented sugar cane - "biofuel" as it is a renewable resource (but still concerns about deforestation). - Oxy-acetylene is the fuel used in metal welding (but it does not release CO2 into the atmosphere) - C2H2 + O2 → 2CO + H2 ### Alcohols You need to know how to draw & name alcohols (up to 4 carbons long) and describe their properties and reactions. - **General info:** - hydroxyl functional group (-O-H) - '-ol' in their name - CnH2n+1OH As they are part of the same homologous series, there is a gradual change in their physical properties e.g. boiling point (due to the length of their hydrocarbon chain), but they have similar chemical properties (due to the same functional group). - **Alcohols are used in alcoholic drinks, fuels, a good solvent (e.g. in paints, glues, perfumes) and as a raw material for making other organic compounds.** - **The hydrocarbon section of the alcohol can combust** - **The -O-H group:** - Causes molecules to stick together so that they are liquid at room temperature - Allows them to mix with water (miscible) - Means that they react with alkali metals like water to form hydrogen, but much more slowly - **Methods of ethanol production:** - Hydration of ethene - Fermentation **Catalytic Hydration of ethene:** - ethene + steam - 300°C, 60 atmospheres phosphoric acid - ethanol - C₂H₄(g) + H₂O(g) → C₂H₂OH(g) **Fermentation:** - Happens best at 37°C. Ethanol and CO2 - natural waste products of yeast when they ferment sugar (anaerobic respiration) - Allows industry to turn alkenes into alcohols. ### Addition Polymerisation Turning small single units (monomers) into long chain molecules (polymers). This is possible because of the C=C in alkenes, which open and join with other monomers. The choice of monomer and how they are linked changes the properties of the polymer. - Many of these addition polymers are **non-biodegradable**, which leads to environmental concerns e.g. litter, filling of landfill sites, build-up of plastics in the oceans. **Steps in drawing the polymer if given the monomer** - Redraw the monomer but with a C-C instead of C=C - Put square brackets around it [] - Where the C=C was, draw continuation bonds going through the brackets - Add a small 'n' on the bottom right - **Reverse this process if asked to draw the monomer** - **Ensure you draw the number of repeating units asked for in the question** **Naming the polymer: poly(monomer) e.g. ethene → poly(ethene)** ### Alkenes You need to know how to draw & name alkenes (up to 4 carbons long) and describe their properties and reactions. - Alkenes are described as unsaturated hydrocarbons with at least one C=C double covalent bond. - **General info:** - functional group (C=C) - '-ene' in their name - CnH2n You can distinguish alkenes from alkanes in the following ways: - Add aqueous bromine (bromine water). - Decolourises in alkenes (red/brown → colourless), remains red/brown in alkanes - Alkenes burn with a smokier/dirtier flame Alkenes can combust too but are more reactive than alkanes due to their C=C, and so take part in addition reactions as well (two molecules joining to make one new product). **You need to know about four addition reactions:** - + Br2 "bromination" - + H₂ "hydrogenation" - +H2O (steam) "hydration" - Addition polymerisation **Bromination** Spontaneous at room temperature and pressure, the C=C bond breaks, the bromine molecule splits in half and joins on (one to each carbon). As elemental bromine is no longer there, we no longer see the red/brown colour from the start. **Hydrogenation** The C=C bond breaks, the hydrogen molecule splits in half and joins on (one to each carbon). A saturated alkane is formed. - Nickel catalyst required! - Allows industry to turn vegetable oils into margarine (now spreadable due to higher melting point) **Hydration** The C=C bond breaks, the water molecule splits in half and joins on (H to one carbon, O-H to the other). An alcohol is formed. - Phosphoric acid catalyst required, very high temperature (300°C) and pressure (60/70atm).