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O-Level Organic Chemistry
fuels and crude oil, hydrocarbons, alcohols, carboxylic acids and esters, and polymers. When describing reactions, students should quote the reagents (for example aqueous bromine) and the essential conditions (for example high temperature and pressure), but exact temperature and pressure figures are not needed.
What the syllabus expects
- Name crude oil and natural gas, which is mostly methane, as sources of energy that are non-renewable.
- Explain that crude oil is a hydrocarbon mixture, split by fractional distillation into fractions that are wanted both as fuels and as feedstock for making chemicals.
- Describe biofuel, such as bioethanol made from sugarcane, as a renewable substitute for crude oil and natural gas.
- Explain why biofuel can be more environmentally sustainable than fossil fuels where carbon dioxide emission is concerned.
- Define a homologous series as compounds sharing a general formula and similar chemical properties, whose physical properties (such as viscosity and melting and boiling points) shift steadily as the molecules grow larger and heavier.
- Describe the alkanes as a saturated-hydrocarbon homologous series whose general formula is CnH2n+2.
- Draw both branched and straight-chain alkanes from C1 to C4 and name the unbranched ones from methane through butane.
- Define isomerism and pick out isomers.
- Describe alkanes, exemplified by methane, as generally unreactive apart from combustion and substitution by chlorine.
- Describe the alkenes as an unsaturated-hydrocarbon homologous series whose general formula is CnH2n.
- Draw both branched and straight-chain alkenes from C2 to C4 and name the unbranched ones from ethene through butene.
- Describe how cracking hydrocarbons produces alkenes and hydrogen, and recognise that cracking is needed to meet demand for the smaller-molecule fractions from refining.
- Distinguish saturated from unsaturated hydrocarbons using their molecular structures and the aqueous bromine test.
- Set out how alkenes react, taking ethene as the example, including combustion, polymerisation, and addition of bromine, steam and hydrogen.
- State what 'polyunsaturated' means when it is applied to food products.
- Describe the manufacture of margarine by adding hydrogen to unsaturated vegetable oils to give a solid product.
- Describe the alcohols as a homologous series that contains the –OH group.
- Draw both branched and straight-chain alcohols from C1 to C4 and name the unbranched ones from methanol through butanol.
- Describe the reactions of alcohols, covering combustion and oxidation into carboxylic acids.
- Describe two routes to ethanol: catalytically adding steam to ethene, and fermenting glucose.
- The carboxylic acids form a homologous series distinguished by the –CO2H group.
- Draw carboxylic acid structures for C1 through C4 and give the names of the straight-chain acids from methanoic acid to butanoic acid.
- Describe the carboxylic acids as weak acids that react with carbonates, bases and some metals.
- Describe how ethanoic acid forms when ethanol is oxidised by atmospheric oxygen or by acidified potassium manganate(VII).
- Describe how a carboxylic acid reacts with an alcohol to form an ester, for instance ethyl ethanoate.
- Given an unbranched C1 to C4 carboxylic acid together with a C1 to C4 alcohol, deduce the ester's name and formula, and work the other way too.
- Describe polymers as big molecules built from small repeating units called monomers, where different polymers differ in their units and/or the linkages joining them.
- Explain how poly(ethene) is produced by addition polymerisation, with ethene serving as the monomer.
- List a few everyday uses of poly(ethene), a typical plastic, for example clingfilm and plastic bags.
- Deduce a polymer's structure from a given monomer, and work backwards too.
- Explain that nylon, a polyamide, and Terylene, a polyester, are both condensation polymers, and give the partial structures for each.
Scope: The details of manufacture and the mechanisms of these polymerisations are not required. - List common applications of synthetic fibres like nylon and Terylene, for instance clothing, curtains, fishing line, parachutes and sleeping bags.
- Describe the pollution problems that arise from disposing of non-biodegradable plastics.
- Describe two plastic-recycling approaches: a physical one, such as melting scraps of poly(ethene) waste down into pellets, and a chemical one, such as depolymerising and cracking plastic waste to give chemical feedstock and fuel respectively.
- Describe depolymerisation as breaking polymers back down into their monomers, exemplified by the acid-catalysed hydrolysis of polyesters.
Scope: Mechanism details are not required. - Discuss the social, economic and environmental issues involved in recycling plastics.
How it's examined
Questions on this topic most often ask you to outline. About 11% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (3 marks)
Cracking can also produce pent-2-ene, whose structure is CH3CH=CHCH2CH3. (c) Draw the two addition polymers obtainable from pent-2-ene, each showing two repeat units.
Show the worked answer
Addition polymerisation opens the C2=C3 double bond of pent-2-ene (CH3-CH=CH-CH2CH3), giving the repeat unit -CH(CH3)-CH(C2H5)- (a methyl group on one backbone carbon, an ethyl group on the next). Because the monomer is unsymmetrical, the units can join in two ways. Polymer 1 - head-to-tail (units all the same way round), two repeat units: -[ -CH(CH3)-CH(C2H5)- ]-[ -CH(CH3)-CH(C2H5)- ]- Polymer 2 - head-to-head / tail-to-tail (alternate units reversed), two repeat units: -[ -CH(CH3)-CH(C2H5)- ]-[ -CH(C2H5)-CH(CH3)- ]- In both, the backbone is fully single-bonded (saturated) and the chain continues at each end (shown with continuation bonds / n).
Example 2 (2 marks)
From the information given, decide whether siloxanes are saturated or unsaturated. Outline a chemical test you could use to check your conclusion. [2] [Total: 4]
Show the worked answer
Siloxanes have a backbone of alternating silicon and oxygen atoms joined by single bonds (Si-O-Si), with the silicon atoms also bonded to carbon/hydrogen groups by single bonds. There are no carbon-carbon double bonds (C=C) or other multiple bonds, so siloxanes are SATURATED. Chemical test for saturation: add a few drops of bromine water (aqueous bromine) to the compound and shake. - If SATURATED (as here): the bromine water is NOT decolourised - it stays orange/brown, because there is no C=C bond to add across. - If UNSATURATED: the orange-brown bromine water would be rapidly decolourised (turns colourless) as bromine adds across the double bond. (Acidified KMnO4 remaining purple / not decolourised is an acceptable alternative test.)
More O-Level Pure Chemistry topics
Experimental Chemistry · The Particulate Nature of Matter · Chemical Bonding and Structure · Chemical Calculations · Acid-Base Chemistry · Qualitative Analysis · all of O-Level Pure Chemistry