Organic Chemistry

• Molecular formula counts. Displayed formula draws. If you can point at every bond, it is displayed — and if you cannot, it is not.
• A homologous series is a family of similar compounds with similar chemical properties, because they share the same functional group. Four general formulae, one rule each: put a number in for n and a real compound comes out.
• Saturated means every carbon-to-carbon bond is single. Unsaturated means at least one of them is not. Look only at carbon-to-carbon bonds — a C=O never counts.
• Isomers means same molecular formula, different connectivity. Rotating the page changes neither.
• Stem from the carbon count. Suffix from the functional group, and the suffix read backwards gives you the family. At Core the list is five compounds long — methane, ethane, ethene, ethanol, ethanoic acid — plus whatever the reactions in 11.4 to 11.7 produce.
• Number only when there is a real choice. For an ester: alkyl from the alcohol first, alkanoate from the acid second.
• Petroleum is a mixture, so a physical process can separate it. Hot at the bottom, cool at the top. Going up: chains shorter, boiling point lower, volatility higher, viscosity lower.
• Alkanes: carbon and hydrogen only, single covalent bonds throughout, generally unreactive. Two exceptions, both named by the syllabus: they burn, and chlorine substitutes them.

• Core 11.1.1 Draw and interpret a displayed formula, showing every atom and every bond — including the O–H that “OH” hides.
• Core 11.1.2 Write and interpret the general formulae of alkanes, alkenes, alcohols and carboxylic acids, and put a number in for n to generate a real compound.
• Core 11.1.3 Identify a functional group as the atom or group of atoms that determines a homologous series’ chemical properties, and locate one in a structure you have not met.
• Core 11.1.4 State that a homologous series is a family of similar compounds with similar chemical properties, due to the presence of the same functional group.
• Core 11.1.5 State what a saturated compound is, in terms of carbon–carbon bonds rather than hydrogen count.
• Core 11.1.6 State what an unsaturated compound is, and identify the carbon–carbon bond that makes it so.
• Core 11.2.1 Name and draw the displayed formulae of methane, ethane, ethene, ethanol and ethanoic acid — and of the organic products of the reactions in 11.4 to 11.7.
• Core 11.2.2 State which family a compound belongs to, from a name ending in -ane, -ene, -ol or -oic acid, or from a molecular or displayed formula.
• Core 11.3.1 Name coal, natural gas and petroleum as the fossil fuels.
• Core 11.3.2 Name methane as the main constituent of natural gas.
• Core 11.3.3 State that hydrocarbons contain hydrogen and carbon only.
• Core 11.3.4 State that petroleum is a mixture of hydrocarbons.
• Core 11.3.5 Describe the separation of petroleum into useful fractions by fractional distillation.
• Core 11.3.6 Describe all four column trends from bottom to top — decreasing chain length, higher volatility, lower boiling points, lower viscosity — each with its direction stated.
• Core 11.3.7 Name the use of every one of the eight fractions, from refinery gas to bitumen, in the syllabus’s own words.
• Core 11.4.1 State that the bonding in alkanes is single covalent and that alkanes are saturated hydrocarbons.
• Core 11.4.2 Describe alkanes as generally unreactive, and name the two exceptions: combustion, and substitution by chlorine.
• Core 11.5.1 State that the bonding in alkenes includes a double carbon–carbon covalent bond, and that alkenes are unsaturated hydrocarbons.
• Core 11.5.2 Describe the manufacture of alkenes and hydrogen by cracking larger alkane molecules, using a high temperature and a catalyst.
• Core 11.5.3 Describe the reasons why cracking is carried out.
• Core 11.5.4 Describe the aqueous bromine test that distinguishes a saturated from an unsaturated hydrocarbon, using the exact observation wording.
• Core 11.6.1 Describe both manufacturing routes to ethanol with all of their conditions: fermentation of aqueous glucose at 25–35 °C with yeast and no oxygen, and catalytic addition of steam to ethene at 300 °C and 6000 kPa with an acid catalyst.
• Core 11.6.2 Describe the combustion of ethanol, counting the oxygen atom already inside the molecule when you balance it.
• Core 11.6.3 State the two uses of ethanol: as a solvent, and as a fuel.
• Core 11.7.1 Describe the reaction of ethanoic acid with metals, with bases and with carbonates, giving the name and the formula of every salt produced.
• Core 11.8.1 Define polymers as large molecules built up from many smaller molecules called monomers.
• Core 11.8.2 Describe the formation of poly(ethene) from ethene monomers, as an example of addition polymerisation.
• Core 11.8.3 State that plastics are made from polymers.
• Core 11.8.4 Describe how the properties of plastics have implications for their disposal.
• Core 11.8.5 Describe the three environmental challenges caused by plastics: landfill, accumulation in oceans, and toxic gases from burning.
• Supplement 11.1.7 State that a structural formula is an unambiguous description of how the atoms in a molecule are arranged, and read all three named examples: CH2=CH2, CH3CH2OH and CH3COOCH3.
• Supplement 11.1.8 Define structural isomers, and deduce both isomers of C4H10 and both of C4H8, proving each pair genuinely different.
• Supplement 11.1.9 Describe all five general characteristics of a homologous series, and give a named example of each.
• Supplement 11.2.3 Name and draw the structural and displayed formulae of unbranched alkanes, alkenes, alcohols and carboxylic acids up to four carbons — including but-1-ene, but-2-ene, propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol.
• Supplement 11.2.4 Name and draw the displayed formulae of the unbranched esters made from unbranched alcohols and carboxylic acids of up to four carbons each.
• Supplement 11.4.3 State that in a substitution reaction one atom or group of atoms is replaced by another.
• Supplement 11.4.4 Describe the substitution of alkanes by chlorine as a photochemical reaction, with ultraviolet light providing the activation energy, and draw the monosubstitution products.
• Supplement 11.5.5 State that in an addition reaction only one product is formed.
• Supplement 11.5.6 Describe the addition reactions of alkenes with bromine, with hydrogen over a nickel catalyst and with steam over an acid catalyst, and draw the product of each.
• Supplement 11.6.4 Describe the advantages and disadvantages of making ethanol by fermentation and by the catalytic addition of steam to ethene, as a genuine like-for-like comparison.
• Supplement 11.7.2 Describe the formation of ethanoic acid by oxidising ethanol, both with acidified aqueous potassium manganate(VII) and by bacterial oxidation during vinegar production.
• Supplement 11.7.3 Describe the reaction of a carboxylic acid with an alcohol, using an acid catalyst, to form an ester.
• Supplement 11.8.6 Identify the repeat units and linkages in addition polymers and in condensation polymers.
• Supplement 11.8.7 Deduce the structure or repeat unit of an addition polymer from a given alkene, and the alkene from a given repeat unit.
• Supplement 11.8.8 Deduce a condensation polymer from its monomers and vice versa, for polyamides from a dicarboxylic acid and a diamine, and polyesters from a dicarboxylic acid and a diol.
• Supplement 11.8.9 Describe the differences between addition and condensation polymerisation.
• Supplement 11.8.10 Describe and draw the structure of nylon, a polyamide, and of PET, a polyester.
• Supplement 11.8.11 State that PET can be converted back into monomers and re-polymerised — without inventing a mechanism for how.
• Supplement 11.8.12 Describe proteins as natural polyamides formed from amino acid monomers, and draw the general amino acid structure with its R side chain.
• Supplement 11.8.13 Describe and draw the structure of a protein, as a chain section showing the amide linkages.

Why classify the errors rather than just re-reading? A recall gap is fixed by the Level 1 prompts. An application error is fixed by the reaction map laboratory, where the whole exercise is deciding which rule applies. A communication error is fixed by the mistake clinic, in about ten minutes. Rereading the chapter fixes none of them efficiently, because it spends the same time on material you already hold.

• “The displayed formula of ethanol is CH3CH2OH.” Core 11.1.1 why it fails That is a structural formula. It compresses C–H and O–H bonds into text instead of drawing them. correct A displayed formula shows every atom and every bond as a line, including the O–H bond that “OH” hides. Taught in 11.1A.
• “Here is butane drawn straight, and here it is drawn bent round a corner — two isomers.” Supplement 11.1.8 why it fails Isomerism is about connectivity, not about the shape of the drawing. Bending the page does not move any atom onto a different neighbour. correct To make a real isomer of C4H10 you must detach a carbon from the end of the chain and attach it to a middle carbon, giving 2-methylpropane. Taught in 11.1C.
• “The alkene with four carbons is called butene.” Supplement 11.2.3 why it fails With four carbons there is more than one place the double bond can sit, so the name is ambiguous. correct Give the locant: but-1-ene has the C=C between carbons 1 and 2; but-2-ene has it between carbons 2 and 3. Taught in 11.2.
• “Ethanol plus methanoic acid gives ethyl methanoic acid.” Supplement 11.2.4 why it fails An ester name never keeps the word “acid”, and the two halves are easy to swap. correct Alkyl from the alcohol first, alkanoate from the acid second: ethanol gives “ethyl”, methanoic acid gives “methanoate”, so the ester is ethyl methanoate. Taught in 11.2.
• “Petroleum is a compound that is broken down in the fractionating column.” Core 11.3.4Core 11.3.5 why it fails Two errors at once: petroleum is not a compound, and distillation does not break anything down. correct Petroleum is a mixture of hydrocarbons. Fractional distillation separates that mixture using differences in boiling point. No bonds inside the molecules are broken. Taught in 11.3.
• “Kerosene boils at 180 °C.” Core 11.3.6 why it fails A fraction is itself a mixture of hydrocarbons of similar chain length, so it does not have one fixed boiling point, and the syllabus supplies no numbers. correct Fractions condense over a range of boiling points. Answer in terms of higher and lower, not in invented degrees. Taught in 11.3.
• “The top of the fractionating column is the hottest part.” Core 11.3.6 why it fails It is the reverse. Vapours rise, cool as they go, and condense when they reach their own boiling range. correct The column is hottest at the bottom and coolest at the top, which is why the short, low-boiling molecules travel furthest up. Taught in 11.3.
• “The bromine water turns clear.” Core 11.5.4 why it fails “Clear” means see-through. Orange bromine water is already clear — you can read print through it. Saying it turned clear describes no change at all. correct Write “the orange-brown colour is decolourised”, or “turns colourless”. Taught in 11.5A.
• “Ethene plus bromine gives 1,2-dibromoethane and hydrogen bromide.” Supplement 11.5.5 why it fails That second product is imported from substitution. In an addition reaction there is nothing left over to form it. correct An addition reaction forms only one product. Every atom of both reactants ends up in that single molecule. Taught in 11.5B.
• “Ultraviolet light is the catalyst for the reaction between methane and chlorine.” Supplement 11.4.4 why it fails A catalyst is a substance that is present at the end unchanged. Light is not a substance. correct Ultraviolet light supplies the activation energy the reaction needs to start. Call it a condition, never a catalyst. Taught in 11.4.
• “Air is bubbled through the fermentation mixture to keep the yeast alive.” Core 11.6.1 why it fails With oxygen present, the process is no longer fermentation, and any ethanol that does form can be oxidised further. correct Fermentation requires the absence of oxygen, with yeast, aqueous glucose and a temperature of 25–35 °C. Taught in 11.6.
• “Ethene is hydrated at 300 °C and 60 kPa.” Core 11.6.1 why it fails A unit slip by a factor of 100. 60 kPa is below atmospheric pressure — a partial vacuum, not a high-pressure plant. correct 6000 kPa, which is the same as 60 atm. Write one or the other, and check the unit before you leave the question. Taught in 11.6.
• “Ethanoic acid reacts with sodium carbonate to give hydrogen.” Core 11.7.1 why it fails The “acid makes a gas, so the gas is hydrogen” shortcut. Which gas depends entirely on what the acid met. correct Metal → hydrogen. Base → water, no gas. Carbonate → carbon dioxide and water. Taught in 11.7A.
• “The repeat unit of poly(ethene) is [CH2CH2]n.” Supplement 11.8.6 why it fails Written that way, the unit looks like a small closed molecule. A repeat unit is a section cut out of a much longer chain. correct Draw open continuation bonds passing through the brackets on both sides, to show that the chain carries on. Taught in Lesson 11.8C.
• “All polymerisation reactions release water.” Supplement 11.8.9 why it fails This over-generalises from condensation polymers to every polymer. correct Addition polymerisation releases nothing at all — the polymer is the only product. Condensation polymerisation releases a small molecule, and you can only say which one by looking at the functional groups actually being joined. Taught in Lesson 11.8D.
• 1. “The displayed formula of ethanol is CH3CH2OH.” Core 11.1.1 defect A structural formula supplied where a displayed one was demanded. why “Displayed” is a technical requirement, not a style. Every bond must appear as a line, and “OH” hides one. repair Draw the O joined to C by a line and the H joined to that O by another: –O–H. transfer Draw the displayed formula of propan-2-ol and count the bonds. You should reach 11.
• 2. “C4H10 has four isomers — straight, bent up, bent down and zig-zag.” Supplement 11.1.8 defect Counting drawings instead of counting connectivities. why Molecules are not flat or rigid; the angle on the page carries no chemical information. repair For each structure, list how many carbons each carbon is bonded to. Identical lists means the same compound. transfer Show that C5H12 drawn as a straight chain and as an L-shape are the same compound.
• 3. “The four-carbon alkene is called butene.” Supplement 11.2.3 defect A missing locant where more than one position is possible. why With four carbons the C=C can sit between carbons 1–2 or 2–3, giving two different compounds. The name is ambiguous. repair Add the number: but-1-ene or but-2-ene, choosing the numbering that gives the lower value. transfer Explain why propene needs no locant but propan-2-ol does.
• 4. “Ethanol plus methanoic acid gives ethyl methanoic acid.” Supplement 11.2.4 defect The word “acid” retained in an ester name. why An ester is not an acid; it has no acidic hydrogen. The acid's ending becomes -oate. repair Delete “ic acid” and write “ate”: ethyl methanoate. transfer Name the ester from butan-1-ol and propanoic acid, then say which parent gave each word.
• 5. “Fractional distillation breaks petroleum down into its fractions.” Core 11.3.5 defect The verb “breaks down”, which describes a chemical change. why Petroleum is a mixture, and distillation is physical. Every molecule survives intact; nothing is broken. repair Write separates. Reserve “breaks down” for cracking. transfer State one difference in the products of distillation and of cracking that proves one is chemical and the other is not.
• 6. “Naphtha is used as jet fuel.” Core 11.3.7 defect Two adjacent fractions swapped. why Naphtha and kerosene sit next to each other in the column, so a list learned as a chant blurs them. repair Anchor naphtha by what makes it unique: it is the only fraction whose use is not a fuel. It is a chemical feedstock. Kerosene is the jet fuel. transfer Without looking, give the use of every fraction below kerosene.
• 7. “The hottest part of the fractionating column is the top.” Core 11.3.6 defect The temperature gradient inverted. why If the top were hottest, nothing would ever condense there, and the column could not separate anything. repair Hot at the bottom, cool at the top. Vapour rises and cools until it reaches its own boiling range. transfer Explain, from that gradient alone, why bitumen never reaches the top of the column.
• 8. “The bromine water turns clear.” Core 11.5.4 defect “Clear” used where “colourless” is meant. why Clear means transparent. Orange bromine water is already transparent, so this sentence reports no change at all. repair Write “the orange-brown colour is decolourised”, or “turns colourless”. transfer Write the observation for warming ethanol with acidified aqueous potassium manganate(VII), avoiding the same trap.
• 9. “Ethene + Br2 → 1,2-dibromoethane + HBr.” Supplement 11.5.5 defect A second product invented for an addition reaction. why Substitution thinking applied to addition. Nothing was displaced from ethene, so there is nothing to build a second molecule from — and the equation no longer balances. repair Delete the second product. Check by adding the reactant formulae: C2H4 + Br2 = C2H4Br2 exactly. transfer Say how many products form when ethene reacts with steam, and why.
• 10. “Ultraviolet light catalyses the reaction of methane with chlorine.” Supplement 11.4.4 defect A condition described as a catalyst. why A catalyst is a substance present unchanged at the end. Light is not a substance. repair Write “ultraviolet light supplies the activation energy”, and place it above the arrow as a condition. transfer Name a genuine catalyst from this chapter and say what it does that light cannot.
• 11. “Air is bubbled through the fermentation mixture to keep the yeast alive.” Core 11.6.1 defect Oxygen introduced into a process defined by its absence. why Fermentation is what yeast does without oxygen. Admit oxygen and the process is no longer fermentation, so it no longer does the job the syllabus names it for. repair Add four words: “in the absence of oxygen”. transfer Write all four fermentation conditions in one sentence, with the oxygen condition named explicitly.
• 12. “Ethene is hydrated at 300 °C and 60 kPa.” Core 11.6.1 defect A unit error of a factor of 100. why 60 kPa is below atmospheric pressure. The answer describes a partial vacuum rather than a high-pressure plant. repair Write 6000 kPa, or write 60 atm. The number 60 belongs only with “atm”. transfer State both conditions for hydration and both for fermentation, with correct units throughout.
• 13. “Ethanoic acid reacts with sodium carbonate to give hydrogen.” Core 11.7.1 defect One memorised gas applied to all three acid reactions. why The second product is decided by the other reactant. Only a metal releases hydrogen. repair Metal → hydrogen. Base → water, no gas. Carbonate → carbon dioxide and water. transfer Give the observation and the confirming test for the gas in each of the two cases where one is produced.
• 14. “The repeat unit of poly(ethene) is [CH2CH2]n.” Supplement 11.8.6 defect Missing continuation bonds. why Without bonds crossing the brackets, the unit reads as a small closed molecule rather than a section cut from a long chain. repair Draw a bond running out of each bracket: –[–CH2–CH2–]n–. transfer Draw the repeat unit of poly(chloroethene) and mark both continuation bonds.
• 15. “The repeat unit of poly(ethene) is –[–CH2=CH2–]n–.” Supplement 11.8.7 defect The double bond kept after polymerisation. why Opening the C=C is the reaction. If it is still there, nothing has happened — and each backbone carbon would need five bonds: 2 hydrogens, a double bond counting 2, and one continuation bond. repair Change the double line to a single line. Count the bonds on one backbone carbon: it must total four. transfer Take the repeat unit –[–CH2–CHCl–]n– back to its monomer and say what you had to add.
• 16. “The repeat unit of poly(propene) is –[–CH3–CH2–]n–.” Supplement 11.8.7 defect A substituent moved onto the wrong backbone carbon. why In propene the CH3 hangs off the second double-bond carbon. Putting it into the backbone gives a carbon with five bonds. repair –[–CH2–CH(CH3)–]n–. Mark the two double-bond carbons before redrawing, and move nothing else. transfer Deduce the repeat unit of the polymer made from CH2=CHF, keeping the F on its own carbon.
• 17. “Nylon is made from ethanoic acid and an amine.” Supplement 11.8.8 defect Condensation monomers given only one functional group each. why With one reactive end apiece, the two would join once and stop. You would get a small molecule, not a polymer. repair Use a dicarboxylic acid and a diamine: HOOC–□–COOH and H2N–▢–NH2. transfer Explain why an amino acid can build a protein on its own, despite there being only one kind of monomer.
• 18. “C2H5OH + 3.5O2 → 2CO2 + 3H2O.” Core 11.6.2 defect The oxygen atom already inside the ethanol was not counted. why Alcohols differ from alkanes here: they bring one oxygen of their own to the left-hand side. repair Seven oxygen atoms are needed on the right; the ethanol supplies one, so O2 supplies six. The coefficient is 3. transfer Balance the complete combustion of ethanol again from a blank page, remembering its own oxygen, then check your coefficient against 3O2. Optional enrichment: methanol, CH3OH, behaves the same way — but only the combustion of ethanol is required by 0620, so do not learn another alcohol’s equation as though it were examinable.
• 19. “Alkanes are unreactive, so petrol does not really burn well.” Core 11.4.2 defect “Limited reactivity” read as “low vigour”. why The phrase restricts the number of types of reaction alkanes undergo, not how energetically those reactions proceed. repair Write: alkanes take part in few types of reaction — combustion, and substitution with chlorine under ultraviolet light — but combustion is vigorous and exothermic. transfer Explain why alkanes are still the basis of nearly every fuel in the fractionating column.
• 20. “Plastics should not be used because they are bad for the environment.” Core 11.8.4 defect A verdict offered where a mechanism was asked for. why No property is named, no consequence is traced, and nothing in the sentence could be marked right or wrong. repair Name the property, then the consequence: “the C–C and C–H bonds are unreactive, so microorganisms cannot break them down, so the plastic persists in landfill”. transfer Build the same property-to-consequence chain for burning poly(chloroethene).

• Two things decide how Topic 11 reaches you in an examination: which route you are on, which fixes your theory papers, and what output the command word asks for, which fixes what you write. A perfect explanation does not answer a command word that asked you to draw.
• Your route decides your theory papers. It does not change your practical component: experimental skills are assessed for Core and Extended candidates alike, and both routes take either Paper 5 or Paper 6.
• On weightings Those percentages are the weightings of the papers, across the whole syllabus. They are not the weighting of Topic 11, and no topic of this syllabus has a published mark share of its own.
• Extended papers assess Core content as well as Supplement content, because Extended means Core plus Supplement. Of the fifty statements in Topic 11, thirty are Core — an Extended candidate who skips them has skipped the larger part of the topic.
• What the route does not change. Practical work is assessed in its own component for both routes, so every observation in this chapter — the orange-brown to colourless of the aqueous bromine test, the effervescence with a carbonate, the limewater test for the gas — is examinable whichever papers you sit. Do not treat practical detail as Supplement material.
• The command word is the same on both routes. What changes with the route is which chemistry it is applied to.